• simendsjo (15/15) Oct 23 2013 Illegal code is accepted in static if, but not in enum
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (9/23) Oct 23 2013 I don't know whether it is even specified but it feels like a feature to...
• simendsjo (4/34) Oct 23 2013 The question is if it would make sense to allow it for enum as

"simendsjo" <simendsjo gmail.com> writes:

Illegal code is accepted in static if, but not in enum 
declarations. This leads to having three lines when one is 
enough. Is this just an oversight, or by design?

template T(alias A) {
     enum T = true;
}

void main() {
     struct S { }
     static if(__traits(compiles, S.a) && T!(S.a)) // ok
         enum e1 = true;
     else
         enum e1 = false;
     enum e2 = __traits(compiles, S.a) && T!(S.a); // No property 
S.a
}

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 10/23/2013 02:55 AM, simendsjo wrote:
 Illegal code is accepted in static if, but not in enum declarations.
 This leads to having three lines when one is enough. Is this just an
 oversight, or by design?

 template T(alias A) {
      enum T = true;
 }

 void main() {
      struct S { }
      static if(__traits(compiles, S.a) && T!(S.a)) // ok
          enum e1 = true;
      else
          enum e1 = false;
      enum e2 = __traits(compiles, S.a) && T!(S.a); // No property S.a
 }

I don't know whether it is even specified but it feels like a feature to me.

Just like the shortcut behavior of runtime if helps with avoiding 
illegal memory accesses, this helps with avoiding illegal code altogether:

// null access avoided
if ((p !is null) && (p.member == 42))

// illegal code avoided
static if (__traits(compiles, S.a) && (S.a == 42))

Ali

"simendsjo" <simendsjo gmail.com> writes:

On Wednesday, 23 October 2013 at 16:27:47 UTC, Ali Çehreli wrote:
 On 10/23/2013 02:55 AM, simendsjo wrote:
 Illegal code is accepted in static if, but not in enum 
 declarations.
 This leads to having three lines when one is enough. Is this 
 just an
 oversight, or by design?

 template T(alias A) {
     enum T = true;
 }

 void main() {
     struct S { }
     static if(__traits(compiles, S.a) && T!(S.a)) // ok
         enum e1 = true;
     else
         enum e1 = false;
     enum e2 = __traits(compiles, S.a) && T!(S.a); // No 
 property S.a
 }

 I don't know whether it is even specified but it feels like a 
 feature to me.

 Just like the shortcut behavior of runtime if helps with 
 avoiding illegal memory accesses, this helps with avoiding 
 illegal code altogether:

 // null access avoided
 if ((p !is null) && (p.member == 42))

 // illegal code avoided
 static if (__traits(compiles, S.a) && (S.a == 42))

 Ali

The question is if it would make sense to allow it for enum as 
well as static if. As enum is a compile-time constant I think it 
would be consistent.