• Per =?UTF-8?B?Tm9yZGzDtnc=?= (30/30) Jul 23 2020 Why doesn't
• Adam D. Ruppe (8/10) Jul 23 2020 The whole codebase must pass the parser before it even considers
• Per =?UTF-8?B?Tm9yZGzDtnc=?= (18/22) Jul 23 2020 Thanks.

Per =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:

Why doesn't

     static assert(!__traits(compiles, {
         void f() { int[2] _ = [1, 2]; foreach (const auto ref e; 
_) {} }
     }));

compile when

     static assert(__traits(compiles, {
         void f() { int[2] _ = [1, 2]; foreach (const ref e; _) {} 
}
     }));

does?

Doesn't __traits(compiles) support syntactic changes to the 
language that hasn't yet been implemented?

If so, is there some other way of detecting this?

I want these to automatically detect and signal with a failing 
`static assert` when a new language feature has been implemented 
or preview-activated so it can be used.

For comparison see

/** Is `true` iff DIP-1000 checking is enabled via compiler flag 
-dip1000.
  *
  * See_Also: 
https://forum.dlang.org/post/qglynupcootocnnnpmhj forum.dlang.org
  * See_Also: 
https://forum.dlang.org/post/pzddsrwhfvcopfaamvak forum.dlang.org
  */
enum isDIP1000 = __traits(compiles, ()  safe { int x; int* p; p = 
&x; });

which can be used to optionally static tests using 
__traits(compiles) when -dip1000 has been fed to the compiler.

Adam D. Ruppe <destructionator gmail.com> writes:

On Thursday, 23 July 2020 at 13:33:02 UTC, Per Nordlöw wrote:
 Doesn't __traits(compiles) support syntactic changes to the 
 language that hasn't yet been implemented?

The whole codebase must pass the parser before it even considers 
what is in there. So new syntax cannot be detected through this 
or version or anything else.... unless the code is quoted.

If the code is in quotes - as a string - then the parser doesn't 
look at it until it needs to. So you might be able to detect 
using mixin.

__traits(compiles, mixin(" your code here"))

Per =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:

On Thursday, 23 July 2020 at 13:59:39 UTC, Adam D. Ruppe wrote:
 If the code is in quotes - as a string - then the parser 
 doesn't look at it until it needs to. So you might be able to 
 detect using mixin.

 __traits(compiles, mixin(" your code here"))

Thanks.

Solved via mixins as:


 safe pure nothrow  nogc:

private enum hasAutoRefForeach = __traits(compiles, () {
         mixin(`void f() { int[2] _ = [1, 2]; foreach (const auto 
ref e; _) {} }`);
     });

private enum hasRefForeach = __traits(compiles, {
         mixin(`void f() { int[2] _ = [1, 2]; foreach (const ref 
e; _) {} }`);
     });

///
unittest
{
     static assert(hasRefForeach);
     static assert(!hasAutoRefForeach);
}