Why use the params keyword

Question

I know this is a basic question  but I couldn t find an answer   Why use it  if you write a function or a method that s using it  when you remove it the code will still work perfectly  100  as without it  E g   With params   static public int addTwoEach params int   args        int sum   0      foreach  var item in args          sum    item   2      return sum      Without params   static public int addTwoEach int   args        int sum   0      foreach  var item in args         sum    item   2      return sum

User · Answer

One more important thing needs to be highlighted. It's better to use params because it is better for performance. When you call a method with params argument and passed to it nothing:

public void ExampleMethod(params string[] args)
{
// do some stuff
}

call:

ExampleMethod();

Then a new versions of the .Net Framework do this (from .Net Framework 4.6):

ExampleMethod(Array.Empty<string>());

This Array.Empty object can be reused by framework later, so there are no needs to do redundant allocations. These allocations will occur when you call this method like this:

 ExampleMethod(new string[] {});

User · Answer

It allows you to add as many base type parameters in your call as you like   addTwoEach 10  2  4  6    whereas with the second form you have to use an array as parameter  addTwoEach new int    10 2 4 6

User · Answer

params also allows you to call the method with a single argument   private static int Foo params int   args        int retVal   0      Array ForEach args   i    gt  retVal    i       return retVal      i e  Foo 1   instead of Foo new int     1      Can be useful for shorthand in scenarios where you might need to pass in a single value rather than an entire array  It still is handled the same way in the method  but gives some candy for calling this way

User · Answer

Another example  public IEnumerable lt string gt  Tokenize params string   words             var items   Tokenize product Name  product FullName  product Xyz

User · Answer

No need to create overload methods  just use one single method with params as shown below     Call params method with one to four integer constant parameters     int sum0   addTwoEach    int sum1   addTwoEach 1   int sum2   addTwoEach 1  2   int sum3   addTwoEach 3  3  3   int sum4   addTwoEach 2  2  2  2

User · Answer

Using params allows you to call the function with no arguments  Without params   static public int addTwoEach int   args        int sum   0       foreach  var item in args                sum    item   2             return sum     addtwoEach       throws an error   Compare with params   static public int addTwoEach params int   args        int sum   0       foreach  var item in args                sum    item   2             return sum     addtwoEach       returns 0   Generally  you can use params when the number of arguments can vary from 0 to infinity  and use an array when numbers of arguments vary from 1 to infinity

User · Answer

One danger with params Keyword is  if after Calls to the Method have been coded     someone accidentally   intentionally removes one more required Parameters from the Method Signature   and  one more required Parameters immediately prior to the params Parameter prior to the Signature change were Type-Compatible with the params Parameter    those Calls will continue to compile with one more Expressions previously intended for required Parameters being treated as the optional params Parameter   I just ran into the worst possible case of this  the params Parameter was of Type object     This is noteworthy because developers are used to the compiler slapping their wrists with the much  much more common scenario where Parameters are removed from a Method with all required Parameters  because the   of Parameters expected would change    For me  it s not worth the shortcut    Type    without params will work with 0 to infinity   of Parameters without needing Overrides   Worst case is you ll have to add a   new  Type        to Calls where it doesn t apply   Btw  imho  the safest  and most readable practice  is to     pass via Named Parameters  which we can now do even in C   2 decades after we could in VB  P   because    1 1  it s the only way that guarantees prevention of unintended values passed to Parameters after Parameter order  Compatible-Type and or count change after Calls have been coded   1 2  it reduces those chances after a Parameter meaning change  because the likely new identifier name reflecting the new meaning is right next to the value being passed to it   1 3  it avoids having to count commas and jump back  amp  forth from Call to Signature to see what Expression is being passed for what Parameter  and  1 3 1  By the way  this reason alone should be plenty  in terms of avoiding frequent error-prone violations of the DRY Principle just to read the code not to mention also modify it   but this reason can be exponentially more important if there are one more Expressions being Passed that themselves contain commas  i e  Multi-Dimensional Array Refs or Multi-Parameter Function Calls   In that case  you couldn t even use  which even if you could  would still be adding an extra step per Parameter per Method Call  a Find All Occurrences in a Selection feature in your editor to automate the comma-counting for you   1 4  if you must use Optional Parameters  params or not   it allows you to search for Calls where a particular Optional Parameter is Passed  and therefore  most likely is not or at least has the possibility of being not the Default Value      NOTE  Reasons 1 2  and 1 3  can ease and reduce chances of error even on coding the initial Calls not to mention when Calls have to be read and or changed     and    do so ONE - PARAMETER - PER - LINE for better readability  because    2 1  it s less cluttered  and   2 2  it avoids having to scroll right  amp  back left  and having to do so PER -  LINE  since most mortals can t read the left part of multiple lines  scroll right and read the right part     2 3  it s consistent with the  Best Practice  we ve already evolved into for Assignment Statements  because every Parameter Passed is in essence an Assignment Statement  assigning a Value or Reference to a Local Variable    Just like those who follow the latest  Best Practice  in Coding Style wouldn t dream of coding multiple Assignment Statements per line  we probably shouldn t  and won t once  Best Practice  catches up to my  genius   P   do so when Passing Parameters    NOTES     Passing in Variables whose names mirror the Parameters  doesn t help when    1 1  you re passing in Literal Constants  i e  a simple 0 1  false true or null that even   Best Practices   may not require you use a Named Constant for and their purpose can t be easily inferred from the Method name    1 2  the Method is significantly lower-level   more generic than the Caller such that you would not want   be able to name your Variables the same similar to the Parameters  or vice versa   or   1 3  you re re-ordering   replacing Parameters in the Signature that may result in prior Calls still Compiling because the Types happen to still be compatible   Having an auto-wrap feature like VS does only eliminates ONE   2 2  of the 8 reasons I gave above   Prior to as late as VS 2015  it did NOT auto-indent       Really  MS     which increases severity of reason  2 1    VS should have an option that generates Method Call snippets with Named Parameters  one per line of course  P  and a compiler option  that requires Named Parameters  similar in concept to Option Explicit in VB which  btw  the requirement of was prolly once thought equally as outrageous but now is prolly required by   Best Practices     In fact   back in my day      in 1991 just months into my career  even before I was using  or had even seen  a language with Named Parameters  I had the anti-sheeple    just cuz you can  don t mean you should    don t blindly  cut the ends of the roast  sense enough to simulate it  using in-line comments  without having seen anyone do so   Not having to use Named Parameters  as well other syntax that save   precious   source code keystrokes  is a relic of the Punch Card era when most of these syntaxes started   There s no excuse for that with modern hardware and IDE s and much more complex software where readability is much  Much  MUCH more important    Code is read much more often than is written    As long as you re not duplicating non-auto-updated code  every  keystroke saved is likely to cost exponentially more when someone  even yourself  is trying to read it later

User · Answer

Might sound stupid  But Params doesn t allow multidimensional array  Whereas you can pass a multidimensional array to a function

User · Answer

With params you can call your method like this   addTwoEach 1  2  3  4  5     Without params  you can   t   Additionally  you can call the method with an array as a parameter in both cases   addTwoEach new int     1  2  3  4  5       That is  params allows you to use a shortcut when calling the method   Unrelated  you can drastically shorten your method   public static int addTwoEach params int   args        return args Sum     2   args Length

User · Answer

Adding params keyword itself shows that you can pass multiple number of parameters while calling that method which is not possible without using it  To be more specific   static public int addTwoEach params int   args        int sum   0       foreach  var item in args                sum    item   2             return sum      When you will call above method you can call it by any of the following ways    addTwoEach   addTwoEach 1  addTwoEach new int    1  2  3  4      But when you will remove params keyword only third way of the above given ways will work fine  For 1st and 2nd case you will get an error

[c#] Why use the params keyword?

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