Switch statement fall-through should it be allowed

Question

For as long as I can remember I have avoided using switch statement fall-through  Actually  I can t remember it ever entering my consciousness as a possible way to do things as it was drilled into my head early on that it was nothing more than a bug in the switch statement  However  today I ran across some code that uses it by design  which got me immediately wondering what everyone in the community thinks about switch statement fall-through  Is it something that a programming language should explicitly not allow  like C  does  though it supplies a workaround  or is it a feature of any language that is powerful enough to leave in the programmer s hands  Edit  I wasn t specific enough to what I meant by fall-through  I use this type a lot      switch m loadAnimSubCt           case 0          case 1                 Do something             break          case 2          case 3          case 4                 Do something             break        However  I m concerned about something like this     switch m loadAnimSubCt           case 0          case 1                 Do something  but fall through to the other cases                after doing it           case 2          case 3          case 4                 Do something else              break        This way whenever the case is 0  1 it will do everything in the switch statement  I ve seen this by design and I just don t know if I agree that switch statements should be used this way  I think the first code example is very useful and safe  The second seems kind of dangerous

User · Answer

It can be very useful a few times  but in general  no fall-through is the desired behavior  Fall-through should be allowed  but not implicit   An example  to update old versions of some data   switch  version        case 1             Update some stuff     case 2             Update more stuff     case 3             Update even more stuff     case 4             And so on

User · Answer

Have you heard of Duff s device  This is a great example of using switch fallthrough   It s a feature that can be used and it can be abused  like almost all language features

User · Answer

It may depend on what you consider fallthrough   I m ok with this sort of thing   switch  value      case 0      result   ZERO DIGIT      break     case 1    case 3    case 5    case 7    case 9       result   ODD DIGIT       break     case 2    case 4    case 6    case 8       result   EVEN DIGIT       break      But if you have a case label followed by code that falls through to another case label  I d pretty much always consider that evil   Perhaps moving the common code to a function and calling from both places would be a better idea   And please note that I use the C   FAQ definition of  evil

User · Answer

It s a double-edged sword  It is sometimes very useful  but often dangerous   When is it good  When you want 10 cases all processed the same way     switch  c      case 1    case 2                  Do some of the work                    FALLTHROUGH      case 17                  Do something                 break    case 5    case 43                  Do something else                 break      The one rule I like is that if you ever do anything fancy where you exclude the break  you need a clear comment    FALLTHROUGH    to indicate that was your intention

User · Answer

It s a double-edged sword  It is sometimes very useful  but often dangerous   When is it good  When you want 10 cases all processed the same way     switch  c      case 1    case 2                  Do some of the work                    FALLTHROUGH      case 17                  Do something                 break    case 5    case 43                  Do something else                 break      The one rule I like is that if you ever do anything fancy where you exclude the break  you need a clear comment    FALLTHROUGH    to indicate that was your intention

User · Answer

As with anything  if used with care  it can be an elegant tool   However  I think the drawbacks more than justify not to use it  and finally not to allow it anymore  C    Among the problems are    it s easy to  forget  a break it s not always obvious for code maintainers that an omitted break was intentional   Good use of a switch case fall-through   switch  x    case 1  case 2  case 3   Do something  break      Baaaaad use of a switch case fall-through   switch  x    case 1      Some code case 2      Some more code case 3      Even more code     break      This can be rewritten using if else constructs with no loss at all in my opinion   My final word  stay away from fall-through case labels as in the bad example  unless you are maintaining legacy code where this style is used and well understood

User · Answer

Fall-through is really a handy thing  depending on what you re doing  Consider this neat and understandable way to arrange options   switch   someoption      case  a     case  b     case  c          Do something     break     case  d     case  e          Do something else     break      Imagine doing this with if else  It would be a mess

User · Answer

In some instances  using fall-throughs is an act of laziness on the part of the programmer - they could use a series of    statements  for example  but instead use a series of  catch-all  switch cases   That being said  I ve found them to be especially helpful when I know that eventually I m going to need the options anyway  for example in a menu response   but have not yet implemented all the choices  Likewise  if you re doing a fall-through for both  a  and  A   I find it substantially cleaner to use the switch fall-through than a compound if statement   It s probably a matter of style and how the programmers think  but I m not generally fond of removing components of a language in the name of  safety  - which is why I tend towards C and its variants descendants more than  say  Java  I like being able to monkey-around with pointers and the like  even when I have no  reason  to

User · Answer

It s a double-edged sword  It is sometimes very useful  but often dangerous   When is it good  When you want 10 cases all processed the same way     switch  c      case 1    case 2                  Do some of the work                    FALLTHROUGH      case 17                  Do something                 break    case 5    case 43                  Do something else                 break      The one rule I like is that if you ever do anything fancy where you exclude the break  you need a clear comment    FALLTHROUGH    to indicate that was your intention

User · Answer

Fall-through should be used only when it is used as a jump table into a block of code  If there is any part of the code with an unconditional break before more cases  all the case groups should end that way   Anything else is  evil

User · Answer

Have you heard of Duff s device  This is a great example of using switch fallthrough   It s a feature that can be used and it can be abused  like almost all language features

User · Answer

It may depend on what you consider fallthrough   I m ok with this sort of thing   switch  value      case 0      result   ZERO DIGIT      break     case 1    case 3    case 5    case 7    case 9       result   ODD DIGIT       break     case 2    case 4    case 6    case 8       result   EVEN DIGIT       break      But if you have a case label followed by code that falls through to another case label  I d pretty much always consider that evil   Perhaps moving the common code to a function and calling from both places would be a better idea   And please note that I use the C   FAQ definition of  evil

User · Answer

Have you heard of Duff s device  This is a great example of using switch fallthrough   It s a feature that can be used and it can be abused  like almost all language features

User · Answer

Fall-through is really a handy thing  depending on what you re doing  Consider this neat and understandable way to arrange options   switch   someoption      case  a     case  b     case  c          Do something     break     case  d     case  e          Do something else     break      Imagine doing this with if else  It would be a mess

User · Answer

It is powerful and dangerous  The biggest problem with fall-through is that it s not explicit  For example  if you come across frequently-edited code that has a switch with fall-throughs  how do you know that s intentional and not a bug   Anywhere I use it  I ensure that it s properly commented   switch  var        case  first              Fall-through     case  second           i            break

User · Answer

It s a double-edged sword  It is sometimes very useful  but often dangerous   When is it good  When you want 10 cases all processed the same way     switch  c      case 1    case 2                  Do some of the work                    FALLTHROUGH      case 17                  Do something                 break    case 5    case 43                  Do something else                 break      The one rule I like is that if you ever do anything fancy where you exclude the break  you need a clear comment    FALLTHROUGH    to indicate that was your intention

User · Answer

I don t like my switch statements to fall through - it s far too error prone and hard to read   The only exception is when multiple case statements all do exactly the same thing   If there is some common code that multiple branches of a switch statement want to use  I extract that into a separate common function that can be called in any branch

User · Answer

Fall-through should be used only when it is used as a jump table into a block of code  If there is any part of the code with an unconditional break before more cases  all the case groups should end that way   Anything else is  evil

User · Answer

I don t like my switch statements to fall through - it s far too error prone and hard to read   The only exception is when multiple case statements all do exactly the same thing   If there is some common code that multiple branches of a switch statement want to use  I extract that into a separate common function that can be called in any branch

User · Answer

It can be very useful a few times  but in general  no fall-through is the desired behavior  Fall-through should be allowed  but not implicit   An example  to update old versions of some data   switch  version        case 1             Update some stuff     case 2             Update more stuff     case 3             Update even more stuff     case 4             And so on

User · Answer

In some instances  using fall-throughs is an act of laziness on the part of the programmer - they could use a series of    statements  for example  but instead use a series of  catch-all  switch cases   That being said  I ve found them to be especially helpful when I know that eventually I m going to need the options anyway  for example in a menu response   but have not yet implemented all the choices  Likewise  if you re doing a fall-through for both  a  and  A   I find it substantially cleaner to use the switch fall-through than a compound if statement   It s probably a matter of style and how the programmers think  but I m not generally fond of removing components of a language in the name of  safety  - which is why I tend towards C and its variants descendants more than  say  Java  I like being able to monkey-around with pointers and the like  even when I have no  reason  to

User · Answer

I d love a different syntax for fallbacks in switches  something like  errr    switch myParam      case 0 or 1 or 2         Do something      break    case 3 or 4         Do something else      break      Note  This would already be possible with enums  if you declare all cases on your enum using flags  right  It doesn t sound so bad either  the cases could  should   very well be part of your enum already   Maybe this would be a nice case  no pun intended  for a fluent interface using extension methods  Something like  errr     int value   10  value Switch      Case      gt       Do something        new  0  1  2      Case      gt       Do something else      new  3  4      Default      gt       Do the default case           Although that s probably even less readable  P

User · Answer

In some instances  using fall-throughs is an act of laziness on the part of the programmer - they could use a series of    statements  for example  but instead use a series of  catch-all  switch cases   That being said  I ve found them to be especially helpful when I know that eventually I m going to need the options anyway  for example in a menu response   but have not yet implemented all the choices  Likewise  if you re doing a fall-through for both  a  and  A   I find it substantially cleaner to use the switch fall-through than a compound if statement   It s probably a matter of style and how the programmers think  but I m not generally fond of removing components of a language in the name of  safety  - which is why I tend towards C and its variants descendants more than  say  Java  I like being able to monkey-around with pointers and the like  even when I have no  reason  to

User · Answer

It may depend on what you consider fallthrough   I m ok with this sort of thing   switch  value      case 0      result   ZERO DIGIT      break     case 1    case 3    case 5    case 7    case 9       result   ODD DIGIT       break     case 2    case 4    case 6    case 8       result   EVEN DIGIT       break      But if you have a case label followed by code that falls through to another case label  I d pretty much always consider that evil   Perhaps moving the common code to a function and calling from both places would be a better idea   And please note that I use the C   FAQ definition of  evil

User · Answer

As with anything  if used with care  it can be an elegant tool   However  I think the drawbacks more than justify not to use it  and finally not to allow it anymore  C    Among the problems are    it s easy to  forget  a break it s not always obvious for code maintainers that an omitted break was intentional   Good use of a switch case fall-through   switch  x    case 1  case 2  case 3   Do something  break      Baaaaad use of a switch case fall-through   switch  x    case 1      Some code case 2      Some more code case 3      Even more code     break      This can be rewritten using if else constructs with no loss at all in my opinion   My final word  stay away from fall-through case labels as in the bad example  unless you are maintaining legacy code where this style is used and well understood

User · Answer

Have you heard of Duff s device  This is a great example of using switch fallthrough   It s a feature that can be used and it can be abused  like almost all language features

User · Answer

Using fall-through like in your first example is clearly OK  and I would not consider it a real fall-through   The second example is dangerous and  if not commented extensively  non-obvious  I teach my students not to use such constructs unless they consider it worth the effort to devote a comment block to it  which describes that this is an intentional fall-through  and why this solution is better than the alternatives  This discourages sloppy use  but it still makes it allowed in the cases where it is used to an advantage   This is more or less equivalent to what we did in space projects when someone wanted to violate the coding standard  they had to apply for dispensation  and I was called on to advise about the ruling

User · Answer

Fall-through is really a handy thing  depending on what you re doing  Consider this neat and understandable way to arrange options   switch   someoption      case  a     case  b     case  c          Do something     break     case  d     case  e          Do something else     break      Imagine doing this with if else  It would be a mess

User · Answer

I don t like my switch statements to fall through - it s far too error prone and hard to read   The only exception is when multiple case statements all do exactly the same thing   If there is some common code that multiple branches of a switch statement want to use  I extract that into a separate common function that can be called in any branch

User · Answer

As with anything  if used with care  it can be an elegant tool   However  I think the drawbacks more than justify not to use it  and finally not to allow it anymore  C    Among the problems are    it s easy to  forget  a break it s not always obvious for code maintainers that an omitted break was intentional   Good use of a switch case fall-through   switch  x    case 1  case 2  case 3   Do something  break      Baaaaad use of a switch case fall-through   switch  x    case 1      Some code case 2      Some more code case 3      Even more code     break      This can be rewritten using if else constructs with no loss at all in my opinion   My final word  stay away from fall-through case labels as in the bad example  unless you are maintaining legacy code where this style is used and well understood

User · Answer

It is powerful and dangerous  The biggest problem with fall-through is that it s not explicit  For example  if you come across frequently-edited code that has a switch with fall-throughs  how do you know that s intentional and not a bug   Anywhere I use it  I ensure that it s properly commented   switch  var        case  first              Fall-through     case  second           i            break

User · Answer

Using fall-through like in your first example is clearly OK  and I would not consider it a real fall-through   The second example is dangerous and  if not commented extensively  non-obvious  I teach my students not to use such constructs unless they consider it worth the effort to devote a comment block to it  which describes that this is an intentional fall-through  and why this solution is better than the alternatives  This discourages sloppy use  but it still makes it allowed in the cases where it is used to an advantage   This is more or less equivalent to what we did in space projects when someone wanted to violate the coding standard  they had to apply for dispensation  and I was called on to advise about the ruling

User · Answer

It can be very useful a few times  but in general  no fall-through is the desired behavior  Fall-through should be allowed  but not implicit   An example  to update old versions of some data   switch  version        case 1             Update some stuff     case 2             Update more stuff     case 3             Update even more stuff     case 4             And so on

User · Answer

It is powerful and dangerous  The biggest problem with fall-through is that it s not explicit  For example  if you come across frequently-edited code that has a switch with fall-throughs  how do you know that s intentional and not a bug   Anywhere I use it  I ensure that it s properly commented   switch  var        case  first              Fall-through     case  second           i            break

User · Answer

It can be very useful a few times  but in general  no fall-through is the desired behavior  Fall-through should be allowed  but not implicit   An example  to update old versions of some data   switch  version        case 1             Update some stuff     case 2             Update more stuff     case 3             Update even more stuff     case 4             And so on

User · Answer

It may depend on what you consider fallthrough   I m ok with this sort of thing   switch  value      case 0      result   ZERO DIGIT      break     case 1    case 3    case 5    case 7    case 9       result   ODD DIGIT       break     case 2    case 4    case 6    case 8       result   EVEN DIGIT       break      But if you have a case label followed by code that falls through to another case label  I d pretty much always consider that evil   Perhaps moving the common code to a function and calling from both places would be a better idea   And please note that I use the C   FAQ definition of  evil

User · Answer

In some instances  using fall-throughs is an act of laziness on the part of the programmer - they could use a series of    statements  for example  but instead use a series of  catch-all  switch cases   That being said  I ve found them to be especially helpful when I know that eventually I m going to need the options anyway  for example in a menu response   but have not yet implemented all the choices  Likewise  if you re doing a fall-through for both  a  and  A   I find it substantially cleaner to use the switch fall-through than a compound if statement   It s probably a matter of style and how the programmers think  but I m not generally fond of removing components of a language in the name of  safety  - which is why I tend towards C and its variants descendants more than  say  Java  I like being able to monkey-around with pointers and the like  even when I have no  reason  to

User · Answer

As with anything  if used with care  it can be an elegant tool   However  I think the drawbacks more than justify not to use it  and finally not to allow it anymore  C    Among the problems are    it s easy to  forget  a break it s not always obvious for code maintainers that an omitted break was intentional   Good use of a switch case fall-through   switch  x    case 1  case 2  case 3   Do something  break      Baaaaad use of a switch case fall-through   switch  x    case 1      Some code case 2      Some more code case 3      Even more code     break      This can be rewritten using if else constructs with no loss at all in my opinion   My final word  stay away from fall-through case labels as in the bad example  unless you are maintaining legacy code where this style is used and well understood

User · Answer

It is powerful and dangerous  The biggest problem with fall-through is that it s not explicit  For example  if you come across frequently-edited code that has a switch with fall-throughs  how do you know that s intentional and not a bug   Anywhere I use it  I ensure that it s properly commented   switch  var        case  first              Fall-through     case  second           i            break

User · Answer

I don t like my switch statements to fall through - it s far too error prone and hard to read   The only exception is when multiple case statements all do exactly the same thing   If there is some common code that multiple branches of a switch statement want to use  I extract that into a separate common function that can be called in any branch

User · Answer

I d love a different syntax for fallbacks in switches  something like  errr    switch myParam      case 0 or 1 or 2         Do something      break    case 3 or 4         Do something else      break      Note  This would already be possible with enums  if you declare all cases on your enum using flags  right  It doesn t sound so bad either  the cases could  should   very well be part of your enum already   Maybe this would be a nice case  no pun intended  for a fluent interface using extension methods  Something like  errr     int value   10  value Switch      Case      gt       Do something        new  0  1  2      Case      gt       Do something else      new  3  4      Default      gt       Do the default case           Although that s probably even less readable  P

User · Answer

Fall-through is really a handy thing  depending on what you re doing  Consider this neat and understandable way to arrange options   switch   someoption      case  a     case  b     case  c          Do something     break     case  d     case  e          Do something else     break      Imagine doing this with if else  It would be a mess

[coding-style] Switch statement fall-through...should it be allowed?

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Examples related to switch-statement