Proposal: Allow #if to guard switch case clauses

rintaro · 2017-05-10T08:32:03.000Z

Hi evolution community,

This proposal allows you to enclose switch cases with #if directive.
Implementation: https://github.com/apple/swift/pull/9457
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

Allow #if to guard switch case clauses

   - Proposal: SE-NNNN <https://gist.github.com/rintaro/NNNN-filename.md>
   - Authors: Rintaro Ishziaki <https://github.com/rintaro>
   - Review Manager: TBD
   - Status: Awaiting review

<NNNN-conditional-switch-case.md · GitHub;
Introduction

This proposal adds ability to guard switch case clauses with #if directives.

Swift-evolution thread: Not yet
<https://lists.swift.org/pipermail/swift-evolution/>
<NNNN-conditional-switch-case.md · GitHub;
Motivation

When you want to switch cases only for certain compilation condition, say
switching #if os(Linux) guarded enum cases, right now you have to write
switch twice:

enum Operation {
  case output(String)
#if os(Linux)
  case syscall(Syscall)
#endif
}
func execute(operation: Operation) {
#if !os(Linux)
   switch operation {
   case .output(let str):
       print(str)
   }
#else
   switch operation {
   case .output(let str):
       print(str)
   case .syscall(let call):
       call.execute()
   }
#endif
}

This is annoying and error prone.
<NNNN-conditional-switch-case.md · GitHub
solution

This proposal allows #if to guard switch case clauses.

func execute(operation: Operation) {
    switch operation {
    case .output(let str):
        print(str)
#if os(Linux)
    case .syscall(let call):
        call.execute()
#endif
    }
}

<NNNN-conditional-switch-case.md · GitHub
design

This change shouldn't affect existing #if directives *within* case clauses.
This code should works as expected:

func foo(x: MyEnum) {
    switch x {
    case .some(let str):
        doSomething(str)
#if PRINT_SOME
        print(str)
#endif
    case .other:
        doOther()
    }
}

Only if the next token after #if is case or default, the Parser treat it as
guarding case clauses.

func foo(x: MyEnum) {
    switch x {
    case .some(let str):
        doSomething(str)
#if HAS_OTHER
    case .other:
        doOther()
    }
#endif
}

func foo(x: MyEnum) {
    switch x {
    case .some(let str):
        doSomething(str)
#if HAS_OTHER
    default:
        break
#endif
}

Error cases:

    switch x {
    case .some(let str):
        doSomething(str)
#if HAS_OTHER
    case .other:
        doOther()
#else
        doMore() // error: all statements inside a switch must be
covered by a 'case' or 'default'#endif
    }

    switch x {
    case .some(let str):
        doSomething(str)
#if HAS_OTHER
        doMore()
    case .other:
        doOther() // error: 'case' label can only appear inside a
'switch' statement#else
    }

You can guard multiple cases as long as it is guarding whole clauses:

    switch x {
    case .some(let str):
        doSomething(str)
#if HAS_OTHERS
    case .other:
        doOther()
    case .more:
        doMore()
#else
    }

<NNNN-conditional-switch-case.md · GitHub;

Rien · 2017-05-10T09:16:57.000Z

I hope this makes it through without generating a lot of extra discussion. I would love to have this in Swift 4, or the next regular update of xcode.

Regards,
Rien

Site: http://balancingrock.nl
Blog: http://swiftrien.blogspot.com
Github: Balancingrock (Rien) · GitHub
Project: http://swiftfire.nl - A server for websites build in Swift

···

On 10 May 2017, at 10:32, rintaro ishizaki via swift-evolution <swift-evolution@swift.org> wrote:

Hi evolution community,

This proposal allows you to enclose switch cases with if directive.
Implementation: [Parse] Allow #if to guard switch case clauses by rintaro · Pull Request #9457 · apple/swift · GitHub
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

Allow if to guard switch case clauses

  • Proposal: SE-NNNN
  • Authors: Rintaro Ishziaki
  • Review Manager: TBD
  • Status: Awaiting review
Introduction

This proposal adds ability to guard switch case clauses with if directives.

Swift-evolution thread: Not yet

Motivation

When you want to switch cases only for certain compilation condition, say switching if os(Linux) guarded enum cases, right now you have to write switch twice:

enum Operation
{

case output(String
)
#
if os(Linux
)

case syscall
(Syscall)
#
endif

}

func execute(operation
: Operation) {
#
if !os(Linux
)

switch
operation {

case .output(let str):

print
(str)
   }
#
else

switch
operation {

case .output(let str):

print
(str)

case .syscall(let call):

       call.
execute
()
   }
#
endif

}

This is annoying and error prone.

Proposed solution

This proposal allows if to guard switch case clauses.

func execute(operation
: Operation) {

switch
operation {

case .output(let str):

print
(str)
#
if os(Linux
)

case .syscall(let call):

        call.
execute
()
#
endif

    }
}

Detailed design

This change shouldn't affect existing if directives within case clauses. This code should works as expected:

func foo(x
: MyEnum) {

switch
x {

case .some(let str):

doSomething
(str)
#
if
PRINT_SOME

print
(str)
#
endif

case .other:

doOther
()
    }
}

Only if the next token after if is case or default, the Parser treat it as guarding case clauses.

func foo(x
: MyEnum) {

switch
x {

case .some(let str):

doSomething
(str)
#
if
HAS_OTHER

case .other:

doOther
()
    }
#
endif

}

func foo(x
: MyEnum) {

switch
x {

case .some(let str):

doSomething
(str)
#
if
HAS_OTHER

default:

break

#
endif

}

Error cases:

    switch
x {

case .some(let str):

doSomething
(str)
#
if
HAS_OTHER

case .other:

doOther
()
#
else

doMore() // error: all statements inside a switch must be covered by a 'case' or 'default'
#endif

    }

    switch
x {

case .some(let str):

doSomething
(str)
#
if
HAS_OTHER

doMore
()

case .other:

doOther() // error: 'case' label can only appear inside a 'switch' statement
#else

    }

You can guard multiple cases as long as it is guarding whole clauses:

    switch
x {

case .some(let str):

doSomething
(str)
#
if
HAS_OTHERS

case .other:

doOther
()

case .more:

doMore
()
#
else

    }

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

Joe_Groff · 2017-05-10T18:44:57.000Z

Seems reasonable to me.

···

On May 10, 2017, at 1:32 AM, rintaro ishizaki via swift-evolution <swift-evolution@swift.org> wrote:

Hi evolution community,

This proposal allows you to enclose switch cases with if directive.
Implementation: [Parse] Allow #if to guard switch case clauses by rintaro · Pull Request #9457 · apple/swift · GitHub
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

Allow if to guard switch case clauses

  • Proposal: SE-NNNN
  • Authors: Rintaro Ishziaki
  • Review Manager: TBD
  • Status: Awaiting review
Introduction

This proposal adds ability to guard switch case clauses with if directives.

Swift-evolution thread: Not yet

Motivation

When you want to switch cases only for certain compilation condition, say switching if os(Linux) guarded enum cases, right now you have to write switch twice:

enum Operation
{

case output(String
)
#
if os(Linux
)

case syscall
(Syscall)
#
endif

}

func execute(operation
: Operation) {
#
if !os(Linux
)

switch
operation {

case .output(let str):

print
(str)
   }
#
else

switch
operation {

case .output(let str):

print
(str)

case .syscall(let call):

       call.
execute
()
   }
#
endif

}

This is annoying and error prone.

Proposed solution

This proposal allows if to guard switch case clauses.

func execute(operation
: Operation) {

switch
operation {

case .output(let str):

print
(str)
#
if os(Linux
)

case .syscall(let call):

        call.
execute
()
#
endif

    }
}

Detailed design

This change shouldn't affect existing if directives within case clauses. This code should works as expected:

func foo(x
: MyEnum) {

switch
x {

case .some(let str):

doSomething
(str)
#
if
PRINT_SOME

print
(str)
#
endif

case .other:

doOther
()
    }
}

Only if the next token after if is case or default, the Parser treat it as guarding case clauses.

func foo(x
: MyEnum) {

switch
x {

case .some(let str):

doSomething
(str)
#
if
HAS_OTHER

case .other:

doOther
()
    }
#
endif

}

func foo(x
: MyEnum) {

switch
x {

case .some(let str):

doSomething
(str)
#
if
HAS_OTHER

default:

break

#
endif

}

Error cases:

    switch
x {

case .some(let str):

doSomething
(str)
#
if
HAS_OTHER

case .other:

doOther
()
#
else

doMore() // error: all statements inside a switch must be covered by a 'case' or 'default'
#endif

    }

    switch
x {

case .some(let str):

doSomething
(str)
#
if
HAS_OTHER

doMore
()

case .other:

doOther() // error: 'case' label can only appear inside a 'switch' statement
#else

    }

You can guard multiple cases as long as it is guarding whole clauses:

    switch
x {

case .some(let str):

doSomething
(str)
#
if
HAS_OTHERS

case .other:

doOther
()

case .more:

doMore
()
#
else

    }

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

jrose · 2017-05-10T18:47:23.000Z

I'm in favor, certainly. I'd personally say this wouldn't even need to go through the full evolution process, but I'm not a core team member.

Jordan

···

On May 10, 2017, at 01:32, rintaro ishizaki via swift-evolution <swift-evolution@swift.org> wrote:

Hi evolution community,

This proposal allows you to enclose switch cases with if directive.
Implementation: [Parse] Allow #if to guard switch case clauses by rintaro · Pull Request #9457 · apple/swift · GitHub
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

rintaro · 2017-05-10T13:28:22.000Z

Here's proposal link:

github.com

rintaro/swift-evolution/blob/conditional-switch-case/proposals/NNNN-conditional-switch-case.md

# Allow `#if` to guard switch case clauses

* Proposal: [SE-NNNN](NNNN-filename.md)
* Authors: [Rintaro Ishizaki](https://github.com/rintaro)
* Review Manager: TBD
* Status: **Awaiting review**

## Introduction

This proposal adds ability to guard switch `case` clauses with `#if` directives.

Swift-evolution thread: [Allow `#if` to guard switch case clauses](https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170508/036568.html)

## Motivation

When you want to switch cases only for certain compilation condition, say switching `#if os(Linux)` guarded enum cases, right now you have to write `switch` twice:

```swift
enum Operation {
  case output(String)

This file has been truncated. show original

Fixed some typos, including my name :)

···

2017-05-10 17:32 GMT+09:00 rintaro ishizaki <fs.output@gmail.com>:

Hi evolution community,

This proposal allows you to enclose switch cases with if directive.
Implementation: [Parse] Allow #if to guard switch case clauses by rintaro · Pull Request #9457 · apple/swift · GitHub
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

Allow if to guard switch case clauses

   - Proposal: SE-NNNN <https://gist.github.com/rintaro/NNNN-filename.md>
   - Authors: Rintaro Ishziaki <https://github.com/rintaro>
   - Review Manager: TBD
   - Status: Awaiting review

<NNNN-conditional-switch-case.md · GitHub;
Introduction

This proposal adds ability to guard switch case clauses with if
directives.

Swift-evolution thread: Not yet
<https://lists.swift.org/pipermail/swift-evolution/>

<NNNN-conditional-switch-case.md · GitHub;
Motivation

When you want to switch cases only for certain compilation condition, say
switching if os(Linux) guarded enum cases, right now you have to write
switch twice:

enum Operation {
  case output(String)
if os(Linux)
  case syscall(Syscall)
#endif
}
func execute(operation: Operation) {
if !os(Linux)
   switch operation {
   case .output(let str):
       print(str)
   }
#else
   switch operation {
   case .output(let str):
       print(str)
   case .syscall(let call):
       call.execute()
   }
#endif
}

This is annoying and error prone.

<NNNN-conditional-switch-case.md · GitHub
solution

This proposal allows if to guard switch case clauses.

func execute(operation: Operation) {
    switch operation {
    case .output(let str):
        print(str)
if os(Linux)
    case .syscall(let call):
        call.execute()
#endif
    }
}

<NNNN-conditional-switch-case.md · GitHub
design

This change shouldn't affect existing if directives *within* case clauses.
This code should works as expected:

func foo(x: MyEnum) {
    switch x {
    case .some(let str):
        doSomething(str)
if PRINT_SOME
        print(str)
#endif
    case .other:
        doOther()
    }
}

Only if the next token after if is case or default, the Parser treat it
as guarding case clauses.

func foo(x: MyEnum) {
    switch x {
    case .some(let str):
        doSomething(str)
if HAS_OTHER
    case .other:
        doOther()
    }
#endif
}

func foo(x: MyEnum) {
    switch x {
    case .some(let str):
        doSomething(str)
if HAS_OTHER
    default:
        break
#endif
}

Error cases:

    switch x {
    case .some(let str):
        doSomething(str)
if HAS_OTHER
    case .other:
        doOther()
#else
        doMore() // error: all statements inside a switch must be covered by a 'case' or 'default'#endif
    }

    switch x {
    case .some(let str):
        doSomething(str)
if HAS_OTHER
        doMore()
    case .other:
        doOther() // error: 'case' label can only appear inside a 'switch' statement#else
    }

You can guard multiple cases as long as it is guarding whole clauses:

    switch x {
    case .some(let str):
        doSomething(str)
if HAS_OTHERS
    case .other:
        doOther()
    case .more:
        doMore()
#else
    }

<NNNN-conditional-switch-case.md · GitHub;

Chris_Lattner · 2017-05-11T05:37:31.000Z

I agree with Jordan.

-Chris

···

On May 10, 2017, at 11:47 AM, Jordan Rose via swift-evolution <swift-evolution@swift.org> wrote:

I'm in favor, certainly. I'd personally say this wouldn't even need to go through the full evolution process, but I'm not a core team member.

Jordan

On May 10, 2017, at 01:32, rintaro ishizaki via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Hi evolution community,

This proposal allows you to enclose switch cases with if directive.
Implementation: [Parse] Allow #if to guard switch case clauses by rintaro · Pull Request #9457 · apple/swift · GitHub
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

knatt · 2017-05-10T17:49:40.000Z

I support this proposal 100%. In fact, I just ran into this use case.

I’d support extending it to allow partial-case coverage (as long as it doesn’t cross a case: boundary, obviously), e.g.

switch result {
case .success(let object):
    doSomething(with: object)
case .error(let error):
    if debug
    alertUser(error)
    #endif
    handleError(error)
}

I don’t see a reason to prevent that, but if we can just get the current proposal (full cases only) in Swift 4 I’ll be satisfied and just put this on my (large and growing) list of things to bring up for 5.

···

On May 10, 2017, at 6:28 AM, rintaro ishizaki via swift-evolution <swift-evolution@swift.org> wrote:

Here's proposal link:
https://github.com/rintaro/swift-evolution/blob/conditional-switch-case/proposals/NNNN-conditional-switch-case.md

Fixed some typos, including my name :)

2017-05-10 17:32 GMT+09:00 rintaro ishizaki <fs.output@gmail.com <mailto:fs.output@gmail.com>>:
Hi evolution community,

This proposal allows you to enclose switch cases with if directive.
Implementation: [Parse] Allow #if to guard switch case clauses by rintaro · Pull Request #9457 · apple/swift · GitHub
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

Allow if to guard switch case clauses

Proposal: SE-NNNN <https://gist.github.com/rintaro/NNNN-filename.md>
Authors: Rintaro Ishziaki <https://github.com/rintaro>
Review Manager: TBD
Status: Awaiting review
<NNNN-conditional-switch-case.md · GitHub

This proposal adds ability to guard switch case clauses with if directives.

Swift-evolution thread: Not yet <https://lists.swift.org/pipermail/swift-evolution/>
<NNNN-conditional-switch-case.md · GitHub

When you want to switch cases only for certain compilation condition, say switching if os(Linux) guarded enum cases, right now you have to write switch twice:

enum Operation {
  case output(String)
if os(Linux)
  case syscall(Syscall)
#endif
}

func execute(operation: Operation) {
if !os(Linux)
   switch operation {
   case .output(let str):
       print(str)
   }
#else
   switch operation {
   case .output(let str):
       print(str)
   case .syscall(let call):
       call.execute()
   }
#endif
}
This is annoying and error prone.

<NNNN-conditional-switch-case.md · GitHub solution

This proposal allows if to guard switch case clauses.

func execute(operation: Operation) {
    switch operation {
    case .output(let str):
        print(str)
if os(Linux)
    case .syscall(let call):
        call.execute()
#endif
    }
}
<NNNN-conditional-switch-case.md · GitHub design

This change shouldn't affect existing if directives within case clauses. This code should works as expected:

func foo(x: MyEnum) {
    switch x {
    case .some(let str):
        doSomething(str)
if PRINT_SOME
        print(str)
#endif
    case .other:
        doOther()
    }
}
Only if the next token after if is case or default, the Parser treat it as guarding case clauses.

func foo(x: MyEnum) {
    switch x {
    case .some(let str):
        doSomething(str)
if HAS_OTHER
    case .other:
        doOther()
    }
#endif
}
func foo(x: MyEnum) {
    switch x {
    case .some(let str):
        doSomething(str)
if HAS_OTHER
    default:
        break
#endif
}
Error cases:

    switch x {
    case .some(let str):
        doSomething(str)
if HAS_OTHER
    case .other:
        doOther()
#else
        doMore() // error: all statements inside a switch must be covered by a 'case' or 'default'
#endif
    }
    switch x {
    case .some(let str):
        doSomething(str)
if HAS_OTHER
        doMore()
    case .other:
        doOther() // error: 'case' label can only appear inside a 'switch' statement
#else
    }
You can guard multiple cases as long as it is guarding whole clauses:

    switch x {
    case .some(let str):
        doSomething(str)
if HAS_OTHERS
    case .other:
        doOther()
    case .more:
        doMore()
#else
    }

<NNNN-conditional-switch-case.md · GitHub;
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

Nicholas_Maccharoli · 2017-05-11T05:45:22.000Z

I also strongly agree.

I can think of no strong argument against this, was this intentional at one
point or a compiler bug?

- Nick

···

On Thu, May 11, 2017 at 2:37 PM, Chris Lattner via swift-evolution < swift-evolution@swift.org> wrote:

I agree with Jordan.

-Chris

On May 10, 2017, at 11:47 AM, Jordan Rose via swift-evolution < > swift-evolution@swift.org> wrote:

I'm in favor, certainly. I'd personally say this wouldn't even need to go
through the full evolution process, but I'm not a core team member.

Jordan

On May 10, 2017, at 01:32, rintaro ishizaki via swift-evolution < > swift-evolution@swift.org> wrote:

Hi evolution community,

This proposal allows you to enclose switch cases with if directive.
Implementation: [Parse] Allow #if to guard switch case clauses by rintaro · Pull Request #9457 · apple/swift · GitHub
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

John_McCall · 2017-05-11T07:18:03.000Z

I also strongly agree.

I can think of no strong argument against this, was this intentional at one point or a compiler bug?

The language design of if is more complex than it is in C: it is part of the language grammar, not a separate phase of pre-processing, and must be specifically supported in every position it appears.

That said, I agree with Chris and Jordan that supporting if in any simple, sequential position in the grammar is an obvious extension of the existing design and can reasonably be fast-tracked.

Grammatically similar positions where it's hard to dispute the consistency argument for #if: get-set clauses, precedencegroup declarations.

A position which would definitely be more useful to prioritize but where both the language design and the implementation are trickier: attribute lists.

John.

···

On May 11, 2017, at 1:45 AM, Nicholas Maccharoli via swift-evolution <swift-evolution@swift.org> wrote:

- Nick

On Thu, May 11, 2017 at 2:37 PM, Chris Lattner via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
I agree with Jordan.

-Chris

On May 10, 2017, at 11:47 AM, Jordan Rose via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

I'm in favor, certainly. I'd personally say this wouldn't even need to go through the full evolution process, but I'm not a core team member.

Jordan

On May 10, 2017, at 01:32, rintaro ishizaki via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Hi evolution community,

This proposal allows you to enclose switch cases with if directive.
Implementation: [Parse] Allow #if to guard switch case clauses by rintaro · Pull Request #9457 · apple/swift · GitHub
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org <mailto:swift-evolution@swift.org>
https://lists.swift.org/mailman/listinfo/swift-evolution

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org <mailto:swift-evolution@swift.org>
https://lists.swift.org/mailman/listinfo/swift-evolution

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

rintaro · 2017-05-11T15:57:17.000Z

Thank you all!

I also strongly agree.

I can think of no strong argument against this, was this intentional at
one point or a compiler bug?

The language design of if is more complex than it is in C: it is part of
the language grammar, not a separate phase of pre-processing, and must be
specifically supported in every position it appears.

That said, I agree with Chris and Jordan that supporting if in any
simple, sequential position in the grammar is an obvious extension of the
existing design and can reasonably be fast-tracked.

So, can I withdraw my proposal PR on swift-evolution repository now?

Grammatically similar positions where it's hard to dispute the consistency
argument for #if: get-set clauses, precedencegroup declarations.

A position which would definitely be more useful to prioritize but where
both the language design and the implementation are trickier: attribute
lists.

John.

···

2017-05-11 16:18 GMT+09:00 John McCall via swift-evolution < swift-evolution@swift.org>:

On May 11, 2017, at 1:45 AM, Nicholas Maccharoli via swift-evolution < > swift-evolution@swift.org> wrote:

- Nick

On Thu, May 11, 2017 at 2:37 PM, Chris Lattner via swift-evolution < > swift-evolution@swift.org> wrote:

I agree with Jordan.

-Chris

On May 10, 2017, at 11:47 AM, Jordan Rose via swift-evolution < >> swift-evolution@swift.org> wrote:

I'm in favor, certainly. I'd personally say this wouldn't even need to go
through the full evolution process, but I'm not a core team member.

Jordan

On May 10, 2017, at 01:32, rintaro ishizaki via swift-evolution < >> swift-evolution@swift.org> wrote:

Hi evolution community,

This proposal allows you to enclose switch cases with if directive.
Implementation: [Parse] Allow #if to guard switch case clauses by rintaro · Pull Request #9457 · apple/swift · GitHub
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

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Jon_Shier · 2017-05-11T17:35:54.000Z

Just wanted to add that I ran into the if limitations when trying to port Alamofire to Linux, so any enhancements would be most welcome. There was a point where I had to duplicate an entire class because I couldn't use if for just the parts I needed.

Jon

···

On May 11, 2017, at 11:57 AM, rintaro ishizaki via swift-evolution <swift-evolution@swift.org> wrote:

Thank you all!

2017-05-11 16:18 GMT+09:00 John McCall via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>>:

On May 11, 2017, at 1:45 AM, Nicholas Maccharoli via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
I also strongly agree.

I can think of no strong argument against this, was this intentional at one point or a compiler bug?

The language design of if is more complex than it is in C: it is part of the language grammar, not a separate phase of pre-processing, and must be specifically supported in every position it appears.

That said, I agree with Chris and Jordan that supporting if in any simple, sequential position in the grammar is an obvious extension of the existing design and can reasonably be fast-tracked.

So, can I withdraw my proposal PR on swift-evolution repository now?

Grammatically similar positions where it's hard to dispute the consistency argument for #if: get-set clauses, precedencegroup declarations.

A position which would definitely be more useful to prioritize but where both the language design and the implementation are trickier: attribute lists.

John.

- Nick

On Thu, May 11, 2017 at 2:37 PM, Chris Lattner via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
I agree with Jordan.

-Chris

On May 10, 2017, at 11:47 AM, Jordan Rose via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

I'm in favor, certainly. I'd personally say this wouldn't even need to go through the full evolution process, but I'm not a core team member.

Jordan

On May 10, 2017, at 01:32, rintaro ishizaki via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Hi evolution community,

This proposal allows you to enclose switch cases with if directive.
Implementation: [Parse] Allow #if to guard switch case clauses by rintaro · Pull Request #9457 · apple/swift · GitHub
This is one of the oldest SR issue:
[SR-2] Build configuration directives can not wrap switch cases · Issue #42628 · apple/swift · GitHub
[SR-4196] Allow #if (conditional compilation) to guard switch cases · Issue #46779 · apple/swift · GitHub

Thanks!
Rintaro

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swift-evolution@swift.org <mailto:swift-evolution@swift.org>
https://lists.swift.org/mailman/listinfo/swift-evolution

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swift-evolution@swift.org <mailto:swift-evolution@swift.org>
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