How many parameters are too many

Question

Routines can have parameters  that s no news  You can define as many parameters as you may need  but too many of them will make your routine difficult to understand and maintain   Of course  you could use a structured variable as a workaround  putting all those variables in a single struct and passing it to the routine  In fact  using structures to simplify parameter lists is one of the techniques described by Steve McConnell in Code Complete  But as he says      Careful programmers avoid bundling data any more than is logically necessary    So if your routine has too many parameters or you use a struct to disguise a big parameter list  you re probably doing something wrong  That is  you re not keeping coupling loose   My question is  when can I consider a parameter list too big  I think that more than 5 parameters  are too many  What do you think

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It s a known fact that  on average  people can keep 7   - 2 things in their head at a time  I like to use that principle with parameters  Assuming that programmers are all above-average intelligent people  I d say everything 10  is too many   BTW  if parameters are similar in any way  I d put them in a vector or list rather than a struct or class

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According to Jeff Bezos of Amazon fame  no more than can be fed with two pizzas

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One of Alan Perlis s well-known programming epigrams  recounted in ACM SIGPLAN Notices 17 9   September  1982  states that  If you have a procedure with 10 parameters  you probably missed some

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According to Steve McConnell in Code Complete  you should     Limit the number of a routine s   parameters to about seven

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According to me there could be cases where you will exceed 4 or some fixed number  Things to lookout could be    Your Method is doing too much and you need to refactor  You might want to consider using a collection or some data structure  Rethink your class design  maybe some things do not need to be passed around    From an angle of ease of use or ease of reading code  I think when you need to kinda  word wrap  your method signature  that should make you stop and think Unless you feel helpless and all efforts of making the signature smaller lead to no result  Some very good libraries in past and present use more than 4-5 prams

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IMO  the justification for a long param list is that the data or context is dynamic in nature  think of printf    a good example of using varargs  A better way to handle such cases is by passing a stream or xml structure  this again minimises the number of parameters    A machine surely wouldn t mind a large number of arguments  but developers do  also think of the maintenance overhead  the number of unit test cases and validation checks  Designers also hate lengthy args list  more arguments mean more changes to interface definitions  whenever a change is to be done  The questions about the coupling cohesion spring from above aspects

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According to Jeff Bezos of Amazon fame  no more than can be fed with two pizzas

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In Worst 5 Code Snippets  check the second one   quot Is this a constructor quot   It has like over 37    4    150 parameters   Here a programmer wrote this constructor      S ome of you may think yes its a big constructor but he used eclipse automatic code generation tools    NOO  in this constructor there was a tiny bug that I discovered  which made me conclude that this constructor was written by hand   by the way this is only the top part of the constructor  its not complete

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It seems like there are other considerations than mere number  here are some that come to mind      logical relation to the primary purpose of the function vs  one-off settings   If they are just environment flags  bundling can be very handy

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If you start having to mentally count off the parameters in the signature and match them to the call  then it is time to refactor

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My rule of thumb is that I need to be able to remember the parameters long enough to look at a call and tell what it does  So if I can t look at the method and then flip over to a call of a method and remember which parameter does what then there are too many   For me that equates to about 5  but I m not that bright  Your mileage may vary   You can create an object with properties to hold the parameters and pass that in if you exceed whatever limit you set  See Martin Fowler s Refactoring book and the chapter on making method calls simpler

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For me   when the list crosses one line on my IDE  then it s one parameter too many  I want to see all the parameters in one line without breaking eye contact  But that s just my personal preference

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One more than necessary   I don t mean to be glib  but there are some functions that necessarily need quite a few options   For example   void   mmap void  addr  size t len  int prot  int flags  int fildes  off t offset     There are 6 arguments  and every one of them is essential   Furthermore  there s no common link between them to justify bundling them   Maybe you could define  struct mmapargs   but that would worse

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When is something considered so obscene as to be something that can be regulated despite the 1st Amendment guarantee to free speech   According to Justice Potter Stewart   I know it when I see it    The same holds here   I hate making hard and fast rules like this because the answer changes not only depending on the size and scope of your project  but I think it changes even down to the module level   Depending on what your method is doing  or what the class is supposed to represent  it s quite possible that 2 arguments is too many and is a symptom of too much coupling   I would suggest that by asking the question in the first place  and qualifying your question as much as you did  that you really know all of this   The best solution here is not to rely on a hard and fast number  but instead look towards design reviews and code reviews among your peers to identify areas where you have low cohesion and tight coupling   Never be afraid to show your colleagues your work   If you are afraid to  that s probably the bigger sign that something is wrong with your code  and that you already know it

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If I have 7-10 parameters in one routine I look at bundling them into a new class but not if that class would be nothing but a bunch of fields with getters and setters - the new class has to do something other than shuffle values in and out   Otherwise I d rather put up with the long parameter list

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It s a known fact that  on average  people can keep 7   - 2 things in their head at a time  I like to use that principle with parameters  Assuming that programmers are all above-average intelligent people  I d say everything 10  is too many   BTW  if parameters are similar in any way  I d put them in a vector or list rather than a struct or class

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It heavily depends on the environment you re working in  Take for example javascript  In javascript the best way to pass in parameters is using objects with key value pairs  which in practice means you only have one parameter  In other systems the sweet spot will be at three or four   In the end  it all boils down to personal taste

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In Worst 5 Code Snippets  check the second one   quot Is this a constructor quot   It has like over 37    4    150 parameters   Here a programmer wrote this constructor      S ome of you may think yes its a big constructor but he used eclipse automatic code generation tools    NOO  in this constructor there was a tiny bug that I discovered  which made me conclude that this constructor was written by hand   by the way this is only the top part of the constructor  its not complete

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Some code I ve worked with in the past used global variables just to avoid passing too many parameters around   Please don t do that     Usually

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If you start having to mentally count off the parameters in the signature and match them to the call  then it is time to refactor

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97 sounds just about right   Any less and you lose flexibility

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According to Perl Best Practices  3 is okay  4 is too many   It s just a guideline  but in our shop that s what we try to stick to

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In Clean Code   Robert C  Martin devoted four pages to the subject  Here s the gist      The ideal number of arguments for a   function is zero  niladic   Next comes   one  monadic   followed closely by two    dyadic   Three arguments  triadic    should be avoided where possible  More   than three  polyadic  requires very   special justification -- and then   shouldn t be used anyway

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I d draw the limit for public functions at 5 parameters myself   IMHO  long parameter lists are only acceptable in private local helper functions that are only meant to be called from a few specific places in the code   In those cases  you may need to pass a lot of state information along  but readability isn t as big of a concern since only you  or someone who will maintain your code and should understand the fundamentals of your module  have to care about calling that function

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IMO  the justification for a long param list is that the data or context is dynamic in nature  think of printf    a good example of using varargs  A better way to handle such cases is by passing a stream or xml structure  this again minimises the number of parameters    A machine surely wouldn t mind a large number of arguments  but developers do  also think of the maintenance overhead  the number of unit test cases and validation checks  Designers also hate lengthy args list  more arguments mean more changes to interface definitions  whenever a change is to be done  The questions about the coupling cohesion spring from above aspects

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Seven things in short term memory    Name of the function Return value of the function Purpose of the function Parameter 1 Parameter 2 Parameter 3 Parameter 4

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It s a known fact that  on average  people can keep 7   - 2 things in their head at a time  I like to use that principle with parameters  Assuming that programmers are all above-average intelligent people  I d say everything 10  is too many   BTW  if parameters are similar in any way  I d put them in a vector or list rather than a struct or class

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It heavily depends on the environment you re working in  Take for example javascript  In javascript the best way to pass in parameters is using objects with key value pairs  which in practice means you only have one parameter  In other systems the sweet spot will be at three or four   In the end  it all boils down to personal taste

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According to Jeff Bezos of Amazon fame  no more than can be fed with two pizzas

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I think the actual number really depends on what makes logical sense with the context of the function   I agree that around 4-5 parameters starts getting crowded   In the case of setting flags  a great way to handle this situation is to enumerate the values and OR them together

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In Clean Code   Robert C  Martin devoted four pages to the subject  Here s the gist      The ideal number of arguments for a   function is zero  niladic   Next comes   one  monadic   followed closely by two    dyadic   Three arguments  triadic    should be avoided where possible  More   than three  polyadic  requires very   special justification -- and then   shouldn t be used anyway

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One of Alan Perlis s well-known programming epigrams  recounted in ACM SIGPLAN Notices 17 9   September  1982  states that  If you have a procedure with 10 parameters  you probably missed some

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According to me there could be cases where you will exceed 4 or some fixed number  Things to lookout could be    Your Method is doing too much and you need to refactor  You might want to consider using a collection or some data structure  Rethink your class design  maybe some things do not need to be passed around    From an angle of ease of use or ease of reading code  I think when you need to kinda  word wrap  your method signature  that should make you stop and think Unless you feel helpless and all efforts of making the signature smaller lead to no result  Some very good libraries in past and present use more than 4-5 prams

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I think the actual number really depends on what makes logical sense with the context of the function   I agree that around 4-5 parameters starts getting crowded   In the case of setting flags  a great way to handle this situation is to enumerate the values and OR them together

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Thank you very much for all your answers    It was a bit surprising to find people who also think  like I do  that 5 parameters is a good limit for the sanity of the code  Generally  people tend to agree that a limit between 3 and 4 is good rule of thumb  This is reasonable as people usually have a bad time counting more than 4 things   As Milan points  on average people can keep more or less 7 things in their head at a time  But I think that you can t forget that  when you are designing maintaining studying a routine  you have to keep in mind more things than just the parameters  Some people consider that a routine should have as many arguments as it needs to  I agree  but only for a few specific cases  calls to OS APIs  routines where optimization is important  etc   I suggest to hide the complexity of these routines by adding a layer of abstraction just above these calls whenever possible  Nick has some interesting thoughts on this  If you don t want to read his comments  I summarize for you  in a nutshell  it depends      I hate making hard and fast rules like this because the answer changes not only depending on the size and scope of your project  but I think it changes even down to the module level  Depending on what your method is doing  or what the class is supposed to represent  it s quite possible that 2 arguments is too many and is a symptom of too much coupling    The moral here is don t be afraid of showing your code to your peers  discuss with them and try to  identify areas where you have low cohesion and tight coupling   Finally  I think wnoise much agrees with Nick  and concludes his satirical contribution with this poetical vision  see comments below  of the art of programming      Programming is not engineering  Organization of code is an art because it depends on human factors  which depend too much on context for any hard rule

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A function can only have too many parameters if some of the parameters are redundant  If all the parameters are used  the function must have the correct number of parameters  Take this often used function   HWND CreateWindowEx     DWORD dwExStyle    LPCTSTR lpClassName    LPCTSTR lpWindowName    DWORD dwStyle    int x    int y    int nWidth    int nHeight    HWND hWndParent    HMENU hMenu    HINSTANCE hInstance    LPVOID lpParam      That s 12 parameters  9 if you bundle the x y w and h as a rectangle  and there s also the parameters derived from the class name as well  How would you reduce this  Would you want to reduce the number more to the point   Don t let the number of parameters bother you  just make sure it s logical and well documented and let intellisense  help you     Other coding assistants are available

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This answer assumes an OO language   If you re not using one--skip this answer  this is not quite a language-agnostic answer in other words   If you are passing more than 3 or so parameters  especially intrinsic types objects   it s not that it s  Too many  but that you may be missing a chance to create a new object     Look for groups of parameters that get passed into more than one method--even a group passed into two methods almost guarantees that you should have a new object there   Then you refactor functionality into your new object and you wouldn t believe how much it helps both your code and your understanding of OO programming

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A length restriction on a parameter list is just one more restriction  And restriction means applied violence  It sounds funny  but you can be non-violent even when programming  Just let the code dictate the rules  It is obvious that if you have many parameters  the body of the function class method will be big enough to make use of them  And big code snippets usually can be refactored and split into smaller chunks  So you get solution against having many parameters as free bonus  since they are split among the smaller refactored pieces of code

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A length restriction on a parameter list is just one more restriction  And restriction means applied violence  It sounds funny  but you can be non-violent even when programming  Just let the code dictate the rules  It is obvious that if you have many parameters  the body of the function class method will be big enough to make use of them  And big code snippets usually can be refactored and split into smaller chunks  So you get solution against having many parameters as free bonus  since they are split among the smaller refactored pieces of code

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I would base my answer on how often the function is called    If it is an init function that is only ever called once then let it take 10 parms or more  who cares   If it is called a bunch of times per frame then I tend to make a structure and just pass a pointer to it since that tends to be faster   assuming that you are not rebuilding the struct every time as well

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IMO  the justification for a long param list is that the data or context is dynamic in nature  think of printf    a good example of using varargs  A better way to handle such cases is by passing a stream or xml structure  this again minimises the number of parameters    A machine surely wouldn t mind a large number of arguments  but developers do  also think of the maintenance overhead  the number of unit test cases and validation checks  Designers also hate lengthy args list  more arguments mean more changes to interface definitions  whenever a change is to be done  The questions about the coupling cohesion spring from above aspects

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According to Steve McConnell in Code Complete  you should     Limit the number of a routine s   parameters to about seven

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One thing I would point out from a performance perspective is that depending on how you pass parameters to a method  passing lots of parameters by value will slow the program down because each parameter has to be copied and then placed on the stack    Using a single class to encompass all of the parameters would work better because a single parameter passed by reference would be elegant and cleaner  and quicker

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According to Perl Best Practices  3 is okay  4 is too many   It s just a guideline  but in our shop that s what we try to stick to

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IMO  the justification for a long param list is that the data or context is dynamic in nature  think of printf    a good example of using varargs  A better way to handle such cases is by passing a stream or xml structure  this again minimises the number of parameters    A machine surely wouldn t mind a large number of arguments  but developers do  also think of the maintenance overhead  the number of unit test cases and validation checks  Designers also hate lengthy args list  more arguments mean more changes to interface definitions  whenever a change is to be done  The questions about the coupling cohesion spring from above aspects

User · Answer

One of Alan Perlis s well-known programming epigrams  recounted in ACM SIGPLAN Notices 17 9   September  1982  states that  If you have a procedure with 10 parameters  you probably missed some

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Seven things in short term memory    Name of the function Return value of the function Purpose of the function Parameter 1 Parameter 2 Parameter 3 Parameter 4

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It seems like there are other considerations than mere number  here are some that come to mind      logical relation to the primary purpose of the function vs  one-off settings   If they are just environment flags  bundling can be very handy

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One more than necessary   I don t mean to be glib  but there are some functions that necessarily need quite a few options   For example   void   mmap void  addr  size t len  int prot  int flags  int fildes  off t offset     There are 6 arguments  and every one of them is essential   Furthermore  there s no common link between them to justify bundling them   Maybe you could define  struct mmapargs   but that would worse

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According to me there could be cases where you will exceed 4 or some fixed number  Things to lookout could be    Your Method is doing too much and you need to refactor  You might want to consider using a collection or some data structure  Rethink your class design  maybe some things do not need to be passed around    From an angle of ease of use or ease of reading code  I think when you need to kinda  word wrap  your method signature  that should make you stop and think Unless you feel helpless and all efforts of making the signature smaller lead to no result  Some very good libraries in past and present use more than 4-5 prams

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I stop at three parameters as a general rule of thumb  Any more and it s time to pass an array of parameters or a configuration object instead  which also allows for future parameters to be added without changing the API

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I d say as long as you have overloads that have 2-4 than you re good to go up higher if you need it

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I d draw the limit for public functions at 5 parameters myself   IMHO  long parameter lists are only acceptable in private local helper functions that are only meant to be called from a few specific places in the code   In those cases  you may need to pass a lot of state information along  but readability isn t as big of a concern since only you  or someone who will maintain your code and should understand the fundamentals of your module  have to care about calling that function

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I agree with Robert Martin s quote in Clean Code  as cited above   the fewer parameters the better   More than 5-7 parameters and method calls become pretty hard to comprehend   Things get especially bad if some of the parameters are optional  and so take null values   or if all the parameters have the same type  making it even harder to figure out which parameter is which    If you can bundle parameters into cohesive domain objects like Customer and Account  your code will be much more pleasant to work with   There is an edge case  if you have a method call that takes a variable number of parameters which form a logical set  there s less cognitive overhead having more parameters   For example you may need a method that specifies a number of HTTP request retries  in terms of the number of milliseconds between retries   Three retries at 1s  2s  and 3s intervals could be specified as   retries 1000  2000  3000    In this limited case  adding more parameters to a call doesn t increase the mental overload that much   Another consideration is if your language supports named parameter lists and allows you to leave out optional parameters   Larger named parameter lists are easier to comprehend than larger unnamed parameter lists   But I d still err on the side of fewer rather than more parameters

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One more than necessary   I don t mean to be glib  but there are some functions that necessarily need quite a few options   For example   void   mmap void  addr  size t len  int prot  int flags  int fildes  off t offset     There are 6 arguments  and every one of them is essential   Furthermore  there s no common link between them to justify bundling them   Maybe you could define  struct mmapargs   but that would worse

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It heavily depends on the environment you re working in  Take for example javascript  In javascript the best way to pass in parameters is using objects with key value pairs  which in practice means you only have one parameter  In other systems the sweet spot will be at three or four   In the end  it all boils down to personal taste

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If you start having to mentally count off the parameters in the signature and match them to the call  then it is time to refactor

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For me   when the list crosses one line on my IDE  then it s one parameter too many  I want to see all the parameters in one line without breaking eye contact  But that s just my personal preference

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I think the actual number really depends on what makes logical sense with the context of the function   I agree that around 4-5 parameters starts getting crowded   In the case of setting flags  a great way to handle this situation is to enumerate the values and OR them together

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Thank you very much for all your answers    It was a bit surprising to find people who also think  like I do  that 5 parameters is a good limit for the sanity of the code  Generally  people tend to agree that a limit between 3 and 4 is good rule of thumb  This is reasonable as people usually have a bad time counting more than 4 things   As Milan points  on average people can keep more or less 7 things in their head at a time  But I think that you can t forget that  when you are designing maintaining studying a routine  you have to keep in mind more things than just the parameters  Some people consider that a routine should have as many arguments as it needs to  I agree  but only for a few specific cases  calls to OS APIs  routines where optimization is important  etc   I suggest to hide the complexity of these routines by adding a layer of abstraction just above these calls whenever possible  Nick has some interesting thoughts on this  If you don t want to read his comments  I summarize for you  in a nutshell  it depends      I hate making hard and fast rules like this because the answer changes not only depending on the size and scope of your project  but I think it changes even down to the module level  Depending on what your method is doing  or what the class is supposed to represent  it s quite possible that 2 arguments is too many and is a symptom of too much coupling    The moral here is don t be afraid of showing your code to your peers  discuss with them and try to  identify areas where you have low cohesion and tight coupling   Finally  I think wnoise much agrees with Nick  and concludes his satirical contribution with this poetical vision  see comments below  of the art of programming      Programming is not engineering  Organization of code is an art because it depends on human factors  which depend too much on context for any hard rule

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I generally agree with 5  however  if there is a situation where I need more and it s the clearest way to solve the problem  then I would use more

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One thing I would point out from a performance perspective is that depending on how you pass parameters to a method  passing lots of parameters by value will slow the program down because each parameter has to be copied and then placed on the stack    Using a single class to encompass all of the parameters would work better because a single parameter passed by reference would be elegant and cleaner  and quicker

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If I have 7-10 parameters in one routine I look at bundling them into a new class but not if that class would be nothing but a bunch of fields with getters and setters - the new class has to do something other than shuffle values in and out   Otherwise I d rather put up with the long parameter list

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One more than necessary   I don t mean to be glib  but there are some functions that necessarily need quite a few options   For example   void   mmap void  addr  size t len  int prot  int flags  int fildes  off t offset     There are 6 arguments  and every one of them is essential   Furthermore  there s no common link between them to justify bundling them   Maybe you could define  struct mmapargs   but that would worse

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I would base my answer on how often the function is called    If it is an init function that is only ever called once then let it take 10 parms or more  who cares   If it is called a bunch of times per frame then I tend to make a structure and just pass a pointer to it since that tends to be faster   assuming that you are not rebuilding the struct every time as well

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A function can only have too many parameters if some of the parameters are redundant  If all the parameters are used  the function must have the correct number of parameters  Take this often used function   HWND CreateWindowEx     DWORD dwExStyle    LPCTSTR lpClassName    LPCTSTR lpWindowName    DWORD dwStyle    int x    int y    int nWidth    int nHeight    HWND hWndParent    HMENU hMenu    HINSTANCE hInstance    LPVOID lpParam      That s 12 parameters  9 if you bundle the x y w and h as a rectangle  and there s also the parameters derived from the class name as well  How would you reduce this  Would you want to reduce the number more to the point   Don t let the number of parameters bother you  just make sure it s logical and well documented and let intellisense  help you     Other coding assistants are available

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I ll agree with 3 is okay  4 is too many as a guideline  With more then 3 parameters  you are inevitably doing more then one task  More then one tasks should be split into separate methods    However  if I looked at the latest project I ve worked on  the exceptions would abound and most cases would be hard to get down to 3 parameters

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I ll agree with 3 is okay  4 is too many as a guideline  With more then 3 parameters  you are inevitably doing more then one task  More then one tasks should be split into separate methods    However  if I looked at the latest project I ve worked on  the exceptions would abound and most cases would be hard to get down to 3 parameters

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A related question you should be considering is how cohesive the routine is   A large number of parameters may be a smell that s telling you that the routine itself is trying to do too much and hence it s cohesion is suspect   I agree that a hard and fast number of parameters is probably impossible but I would guess that a high cohesion routine would imply a low number of parameters

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I generally agree with 5  however  if there is a situation where I need more and it s the clearest way to solve the problem  then I would use more

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For me   when the list crosses one line on my IDE  then it s one parameter too many  I want to see all the parameters in one line without breaking eye contact  But that s just my personal preference

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According to Perl Best Practices  3 is okay  4 is too many   It s just a guideline  but in our shop that s what we try to stick to

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Thank you very much for all your answers    It was a bit surprising to find people who also think  like I do  that 5 parameters is a good limit for the sanity of the code  Generally  people tend to agree that a limit between 3 and 4 is good rule of thumb  This is reasonable as people usually have a bad time counting more than 4 things   As Milan points  on average people can keep more or less 7 things in their head at a time  But I think that you can t forget that  when you are designing maintaining studying a routine  you have to keep in mind more things than just the parameters  Some people consider that a routine should have as many arguments as it needs to  I agree  but only for a few specific cases  calls to OS APIs  routines where optimization is important  etc   I suggest to hide the complexity of these routines by adding a layer of abstraction just above these calls whenever possible  Nick has some interesting thoughts on this  If you don t want to read his comments  I summarize for you  in a nutshell  it depends      I hate making hard and fast rules like this because the answer changes not only depending on the size and scope of your project  but I think it changes even down to the module level  Depending on what your method is doing  or what the class is supposed to represent  it s quite possible that 2 arguments is too many and is a symptom of too much coupling    The moral here is don t be afraid of showing your code to your peers  discuss with them and try to  identify areas where you have low cohesion and tight coupling   Finally  I think wnoise much agrees with Nick  and concludes his satirical contribution with this poetical vision  see comments below  of the art of programming      Programming is not engineering  Organization of code is an art because it depends on human factors  which depend too much on context for any hard rule

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I ll agree with 3 is okay  4 is too many as a guideline  With more then 3 parameters  you are inevitably doing more then one task  More then one tasks should be split into separate methods    However  if I looked at the latest project I ve worked on  the exceptions would abound and most cases would be hard to get down to 3 parameters

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I d say as long as you have overloads that have 2-4 than you re good to go up higher if you need it

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I stop at three parameters as a general rule of thumb  Any more and it s time to pass an array of parameters or a configuration object instead  which also allows for future parameters to be added without changing the API

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A length restriction on a parameter list is just one more restriction  And restriction means applied violence  It sounds funny  but you can be non-violent even when programming  Just let the code dictate the rules  It is obvious that if you have many parameters  the body of the function class method will be big enough to make use of them  And big code snippets usually can be refactored and split into smaller chunks  So you get solution against having many parameters as free bonus  since they are split among the smaller refactored pieces of code

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According to Steve McConnell in Code Complete  you should     Limit the number of a routine s   parameters to about seven

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Some code I ve worked with in the past used global variables just to avoid passing too many parameters around   Please don t do that     Usually

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When is something considered so obscene as to be something that can be regulated despite the 1st Amendment guarantee to free speech   According to Justice Potter Stewart   I know it when I see it    The same holds here   I hate making hard and fast rules like this because the answer changes not only depending on the size and scope of your project  but I think it changes even down to the module level   Depending on what your method is doing  or what the class is supposed to represent  it s quite possible that 2 arguments is too many and is a symptom of too much coupling   I would suggest that by asking the question in the first place  and qualifying your question as much as you did  that you really know all of this   The best solution here is not to rely on a hard and fast number  but instead look towards design reviews and code reviews among your peers to identify areas where you have low cohesion and tight coupling   Never be afraid to show your colleagues your work   If you are afraid to  that s probably the bigger sign that something is wrong with your code  and that you already know it

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If you start having to mentally count off the parameters in the signature and match them to the call  then it is time to refactor

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In Clean Code   Robert C  Martin devoted four pages to the subject  Here s the gist      The ideal number of arguments for a   function is zero  niladic   Next comes   one  monadic   followed closely by two    dyadic   Three arguments  triadic    should be avoided where possible  More   than three  polyadic  requires very   special justification -- and then   shouldn t be used anyway

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It seems like there are other considerations than mere number  here are some that come to mind      logical relation to the primary purpose of the function vs  one-off settings   If they are just environment flags  bundling can be very handy

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It s a known fact that  on average  people can keep 7   - 2 things in their head at a time  I like to use that principle with parameters  Assuming that programmers are all above-average intelligent people  I d say everything 10  is too many   BTW  if parameters are similar in any way  I d put them in a vector or list rather than a struct or class

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I would base my answer on how often the function is called    If it is an init function that is only ever called once then let it take 10 parms or more  who cares   If it is called a bunch of times per frame then I tend to make a structure and just pass a pointer to it since that tends to be faster   assuming that you are not rebuilding the struct every time as well

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This answer assumes an OO language   If you re not using one--skip this answer  this is not quite a language-agnostic answer in other words   If you are passing more than 3 or so parameters  especially intrinsic types objects   it s not that it s  Too many  but that you may be missing a chance to create a new object     Look for groups of parameters that get passed into more than one method--even a group passed into two methods almost guarantees that you should have a new object there   Then you refactor functionality into your new object and you wouldn t believe how much it helps both your code and your understanding of OO programming

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I generally agree with 5  however  if there is a situation where I need more and it s the clearest way to solve the problem  then I would use more

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I generally agree with 5  however  if there is a situation where I need more and it s the clearest way to solve the problem  then I would use more

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When is something considered so obscene as to be something that can be regulated despite the 1st Amendment guarantee to free speech   According to Justice Potter Stewart   I know it when I see it    The same holds here   I hate making hard and fast rules like this because the answer changes not only depending on the size and scope of your project  but I think it changes even down to the module level   Depending on what your method is doing  or what the class is supposed to represent  it s quite possible that 2 arguments is too many and is a symptom of too much coupling   I would suggest that by asking the question in the first place  and qualifying your question as much as you did  that you really know all of this   The best solution here is not to rely on a hard and fast number  but instead look towards design reviews and code reviews among your peers to identify areas where you have low cohesion and tight coupling   Never be afraid to show your colleagues your work   If you are afraid to  that s probably the bigger sign that something is wrong with your code  and that you already know it

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For me   when the list crosses one line on my IDE  then it s one parameter too many  I want to see all the parameters in one line without breaking eye contact  But that s just my personal preference

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One of Alan Perlis s well-known programming epigrams  recounted in ACM SIGPLAN Notices 17 9   September  1982  states that  If you have a procedure with 10 parameters  you probably missed some

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A related question you should be considering is how cohesive the routine is   A large number of parameters may be a smell that s telling you that the routine itself is trying to do too much and hence it s cohesion is suspect   I agree that a hard and fast number of parameters is probably impossible but I would guess that a high cohesion routine would imply a low number of parameters

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My rule of thumb is that I need to be able to remember the parameters long enough to look at a call and tell what it does  So if I can t look at the method and then flip over to a call of a method and remember which parameter does what then there are too many   For me that equates to about 5  but I m not that bright  Your mileage may vary   You can create an object with properties to hold the parameters and pass that in if you exceed whatever limit you set  See Martin Fowler s Refactoring book and the chapter on making method calls simpler

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I ll agree with 3 is okay  4 is too many as a guideline  With more then 3 parameters  you are inevitably doing more then one task  More then one tasks should be split into separate methods    However  if I looked at the latest project I ve worked on  the exceptions would abound and most cases would be hard to get down to 3 parameters

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A related question you should be considering is how cohesive the routine is   A large number of parameters may be a smell that s telling you that the routine itself is trying to do too much and hence it s cohesion is suspect   I agree that a hard and fast number of parameters is probably impossible but I would guess that a high cohesion routine would imply a low number of parameters

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I stop at three parameters as a general rule of thumb  Any more and it s time to pass an array of parameters or a configuration object instead  which also allows for future parameters to be added without changing the API

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I d draw the limit for public functions at 5 parameters myself   IMHO  long parameter lists are only acceptable in private local helper functions that are only meant to be called from a few specific places in the code   In those cases  you may need to pass a lot of state information along  but readability isn t as big of a concern since only you  or someone who will maintain your code and should understand the fundamentals of your module  have to care about calling that function

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A function can only have too many parameters if some of the parameters are redundant  If all the parameters are used  the function must have the correct number of parameters  Take this often used function   HWND CreateWindowEx     DWORD dwExStyle    LPCTSTR lpClassName    LPCTSTR lpWindowName    DWORD dwStyle    int x    int y    int nWidth    int nHeight    HWND hWndParent    HMENU hMenu    HINSTANCE hInstance    LPVOID lpParam      That s 12 parameters  9 if you bundle the x y w and h as a rectangle  and there s also the parameters derived from the class name as well  How would you reduce this  Would you want to reduce the number more to the point   Don t let the number of parameters bother you  just make sure it s logical and well documented and let intellisense  help you     Other coding assistants are available

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I think the actual number really depends on what makes logical sense with the context of the function   I agree that around 4-5 parameters starts getting crowded   In the case of setting flags  a great way to handle this situation is to enumerate the values and OR them together

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I d draw the limit for public functions at 5 parameters myself   IMHO  long parameter lists are only acceptable in private local helper functions that are only meant to be called from a few specific places in the code   In those cases  you may need to pass a lot of state information along  but readability isn t as big of a concern since only you  or someone who will maintain your code and should understand the fundamentals of your module  have to care about calling that function

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When is something considered so obscene as to be something that can be regulated despite the 1st Amendment guarantee to free speech   According to Justice Potter Stewart   I know it when I see it    The same holds here   I hate making hard and fast rules like this because the answer changes not only depending on the size and scope of your project  but I think it changes even down to the module level   Depending on what your method is doing  or what the class is supposed to represent  it s quite possible that 2 arguments is too many and is a symptom of too much coupling   I would suggest that by asking the question in the first place  and qualifying your question as much as you did  that you really know all of this   The best solution here is not to rely on a hard and fast number  but instead look towards design reviews and code reviews among your peers to identify areas where you have low cohesion and tight coupling   Never be afraid to show your colleagues your work   If you are afraid to  that s probably the bigger sign that something is wrong with your code  and that you already know it

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I d say as long as you have overloads that have 2-4 than you re good to go up higher if you need it

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In Clean Code   Robert C  Martin devoted four pages to the subject  Here s the gist      The ideal number of arguments for a   function is zero  niladic   Next comes   one  monadic   followed closely by two    dyadic   Three arguments  triadic    should be avoided where possible  More   than three  polyadic  requires very   special justification -- and then   shouldn t be used anyway

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I would base my answer on how often the function is called    If it is an init function that is only ever called once then let it take 10 parms or more  who cares   If it is called a bunch of times per frame then I tend to make a structure and just pass a pointer to it since that tends to be faster   assuming that you are not rebuilding the struct every time as well

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A length restriction on a parameter list is just one more restriction  And restriction means applied violence  It sounds funny  but you can be non-violent even when programming  Just let the code dictate the rules  It is obvious that if you have many parameters  the body of the function class method will be big enough to make use of them  And big code snippets usually can be refactored and split into smaller chunks  So you get solution against having many parameters as free bonus  since they are split among the smaller refactored pieces of code

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This answer assumes an OO language   If you re not using one--skip this answer  this is not quite a language-agnostic answer in other words   If you are passing more than 3 or so parameters  especially intrinsic types objects   it s not that it s  Too many  but that you may be missing a chance to create a new object     Look for groups of parameters that get passed into more than one method--even a group passed into two methods almost guarantees that you should have a new object there   Then you refactor functionality into your new object and you wouldn t believe how much it helps both your code and your understanding of OO programming

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According to me there could be cases where you will exceed 4 or some fixed number  Things to lookout could be    Your Method is doing too much and you need to refactor  You might want to consider using a collection or some data structure  Rethink your class design  maybe some things do not need to be passed around    From an angle of ease of use or ease of reading code  I think when you need to kinda  word wrap  your method signature  that should make you stop and think Unless you feel helpless and all efforts of making the signature smaller lead to no result  Some very good libraries in past and present use more than 4-5 prams

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It heavily depends on the environment you re working in  Take for example javascript  In javascript the best way to pass in parameters is using objects with key value pairs  which in practice means you only have one parameter  In other systems the sweet spot will be at three or four   In the end  it all boils down to personal taste

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According to Steve McConnell in Code Complete  you should     Limit the number of a routine s   parameters to about seven

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97 sounds just about right   Any less and you lose flexibility

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This answer assumes an OO language   If you re not using one--skip this answer  this is not quite a language-agnostic answer in other words   If you are passing more than 3 or so parameters  especially intrinsic types objects   it s not that it s  Too many  but that you may be missing a chance to create a new object     Look for groups of parameters that get passed into more than one method--even a group passed into two methods almost guarantees that you should have a new object there   Then you refactor functionality into your new object and you wouldn t believe how much it helps both your code and your understanding of OO programming

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I d say as long as you have overloads that have 2-4 than you re good to go up higher if you need it

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Thank you very much for all your answers    It was a bit surprising to find people who also think  like I do  that 5 parameters is a good limit for the sanity of the code  Generally  people tend to agree that a limit between 3 and 4 is good rule of thumb  This is reasonable as people usually have a bad time counting more than 4 things   As Milan points  on average people can keep more or less 7 things in their head at a time  But I think that you can t forget that  when you are designing maintaining studying a routine  you have to keep in mind more things than just the parameters  Some people consider that a routine should have as many arguments as it needs to  I agree  but only for a few specific cases  calls to OS APIs  routines where optimization is important  etc   I suggest to hide the complexity of these routines by adding a layer of abstraction just above these calls whenever possible  Nick has some interesting thoughts on this  If you don t want to read his comments  I summarize for you  in a nutshell  it depends      I hate making hard and fast rules like this because the answer changes not only depending on the size and scope of your project  but I think it changes even down to the module level  Depending on what your method is doing  or what the class is supposed to represent  it s quite possible that 2 arguments is too many and is a symptom of too much coupling    The moral here is don t be afraid of showing your code to your peers  discuss with them and try to  identify areas where you have low cohesion and tight coupling   Finally  I think wnoise much agrees with Nick  and concludes his satirical contribution with this poetical vision  see comments below  of the art of programming      Programming is not engineering  Organization of code is an art because it depends on human factors  which depend too much on context for any hard rule

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Some code I ve worked with in the past used global variables just to avoid passing too many parameters around   Please don t do that     Usually

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I stop at three parameters as a general rule of thumb  Any more and it s time to pass an array of parameters or a configuration object instead  which also allows for future parameters to be added without changing the API

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According to Perl Best Practices  3 is okay  4 is too many   It s just a guideline  but in our shop that s what we try to stick to

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I agree with Robert Martin s quote in Clean Code  as cited above   the fewer parameters the better   More than 5-7 parameters and method calls become pretty hard to comprehend   Things get especially bad if some of the parameters are optional  and so take null values   or if all the parameters have the same type  making it even harder to figure out which parameter is which    If you can bundle parameters into cohesive domain objects like Customer and Account  your code will be much more pleasant to work with   There is an edge case  if you have a method call that takes a variable number of parameters which form a logical set  there s less cognitive overhead having more parameters   For example you may need a method that specifies a number of HTTP request retries  in terms of the number of milliseconds between retries   Three retries at 1s  2s  and 3s intervals could be specified as   retries 1000  2000  3000    In this limited case  adding more parameters to a call doesn t increase the mental overload that much   Another consideration is if your language supports named parameter lists and allows you to leave out optional parameters   Larger named parameter lists are easier to comprehend than larger unnamed parameter lists   But I d still err on the side of fewer rather than more parameters

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If I have 7-10 parameters in one routine I look at bundling them into a new class but not if that class would be nothing but a bunch of fields with getters and setters - the new class has to do something other than shuffle values in and out   Otherwise I d rather put up with the long parameter list

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It seems like there are other considerations than mere number  here are some that come to mind      logical relation to the primary purpose of the function vs  one-off settings   If they are just environment flags  bundling can be very handy

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If I have 7-10 parameters in one routine I look at bundling them into a new class but not if that class would be nothing but a bunch of fields with getters and setters - the new class has to do something other than shuffle values in and out   Otherwise I d rather put up with the long parameter list

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A related question you should be considering is how cohesive the routine is   A large number of parameters may be a smell that s telling you that the routine itself is trying to do too much and hence it s cohesion is suspect   I agree that a hard and fast number of parameters is probably impossible but I would guess that a high cohesion routine would imply a low number of parameters

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Some code I ve worked with in the past used global variables just to avoid passing too many parameters around   Please don t do that     Usually

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A function can only have too many parameters if some of the parameters are redundant  If all the parameters are used  the function must have the correct number of parameters  Take this often used function   HWND CreateWindowEx     DWORD dwExStyle    LPCTSTR lpClassName    LPCTSTR lpWindowName    DWORD dwStyle    int x    int y    int nWidth    int nHeight    HWND hWndParent    HMENU hMenu    HINSTANCE hInstance    LPVOID lpParam      That s 12 parameters  9 if you bundle the x y w and h as a rectangle  and there s also the parameters derived from the class name as well  How would you reduce this  Would you want to reduce the number more to the point   Don t let the number of parameters bother you  just make sure it s logical and well documented and let intellisense  help you     Other coding assistants are available

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According to Jeff Bezos of Amazon fame  no more than can be fed with two pizzas

[parameters] How many parameters are too many?

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