• SrMordred (3/3) Oct 25 2017 Maybe i´m tired already, but whats wrong here:
• SrMordred (7/10) Oct 25 2017 Or the original case I found:
• Adam D. Ruppe (6/8) Oct 25 2017 The semicolon there indicates it is a complete statement that
• SrMordred (3/5) Oct 25 2017 so why this line resolves to false?
• Adam D. Ruppe (11/14) Oct 25 2017 Because it is illegal to put a statement or declaration inside
• SrMordred (4/18) Oct 25 2017 Oh, now thats explains. I thought that a "mixin statement" was
• Adam D. Ruppe (4/6) Oct 25 2017 You are missing a ;
• SrMordred (20/27) Oct 25 2017 it returns false anyway.

SrMordred <patric.dexheimer gmail.com> writes:

Maybe i´m tired already, but whats wrong here:

pragma(msg, __traits( compiles, mixin("int x") ) );
//output: false

SrMordred <patric.dexheimer gmail.com> writes:

On Wednesday, 25 October 2017 at 19:12:02 UTC, SrMordred wrote:
 Maybe i´m tired already, but whats wrong here:

 pragma(msg, __traits( compiles, mixin("int x") ) );
 //output: false

Or the original case I found:

struct T{}

pragma(msg, __traits( compiles, T() ) ); //true
pragma(msg, __traits( compiles, mixin("T()") ) ); //true
mixin( "T();" ); Error: `structliteral` has no effect in 
expression `T()`

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

On Wednesday, 25 October 2017 at 19:21:27 UTC, SrMordred wrote:
 mixin( "T();" ); Error: `structliteral` has no effect in 
 expression `T()`

The semicolon there indicates it is a complete statement that 
does nothing, and that's no error.

If there's no ;, it is just an expression that must be somewhere 
else - and the compile error is deferred until higher in the call 
chain.

SrMordred <patric.dexheimer gmail.com> writes:

 The semicolon there indicates it is a complete statement that 
 does nothing, and that's no error.

so why this line resolves to false?
void F(){}
pragma(msg, __traits( compiles, mixin("F();") ) );//false

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

On Wednesday, 25 October 2017 at 19:50:31 UTC, SrMordred wrote:
 so why this line resolves to false?

Because it is illegal to put a statement or declaration inside 
__traits(compiles). sorry, I should have said that before... even 
though the mixin can be legal in another context, it won't be in 
the __traits context due to this:

https://dlang.org/spec/traits.html#compiles

"Returns a bool true if all of the arguments compile (are 
semantically correct). The arguments can be symbols, types, or 
expressions that are syntactically correct. The arguments cannot 
be statements or declarations. "


When there's a closing ;, it is a mixin statement.

 void F(){}
 pragma(msg, __traits( compiles, mixin("F();") ) );//false

SrMordred <patric.dexheimer gmail.com> writes:

On Wednesday, 25 October 2017 at 20:04:47 UTC, Adam D. Ruppe 
wrote:
 On Wednesday, 25 October 2017 at 19:50:31 UTC, SrMordred wrote:
 so why this line resolves to false?

 Because it is illegal to put a statement or declaration inside 
 __traits(compiles). sorry, I should have said that before... 
 even though the mixin can be legal in another context, it won't 
 be in the __traits context due to this:

 https://dlang.org/spec/traits.html#compiles

 "Returns a bool true if all of the arguments compile (are 
 semantically correct). The arguments can be symbols, types, or 
 expressions that are syntactically correct. The arguments 
 cannot be statements or declarations. "


 When there's a closing ;, it is a mixin statement.

 void F(){}
 pragma(msg, __traits( compiles, mixin("F();") ) );//false


Oh, now thats explains. I thought that a "mixin statement" was 
equal to the argument type that it compiles to. Thanks!

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

On Wednesday, 25 October 2017 at 19:12:02 UTC, SrMordred wrote:
 Maybe i´m tired already, but whats wrong here:

 pragma(msg, __traits( compiles, mixin("int x") ) );

You are missing a ;

The mixin must compile as a full thing in context. Variable 
declarations need the ; to be complete.

SrMordred <patric.dexheimer gmail.com> writes:

On Wednesday, 25 October 2017 at 19:25:01 UTC, Adam D. Ruppe 
wrote:
 On Wednesday, 25 October 2017 at 19:12:02 UTC, SrMordred wrote:
 Maybe i´m tired already, but whats wrong here:

 pragma(msg, __traits( compiles, mixin("int x") ) );

 You are missing a ;

 The mixin must compile as a full thing in context. Variable 
 declarations need the ; to be complete.

it returns false anyway.

void F(){
   writeln("inside");
}

struct T{}

void main()
{
         pragma(msg, __traits( compiles, mixin("int x;") ) 
);//false

	pragma(msg, __traits( compiles, mixin("F();") ) );//false
	pragma(msg, __traits( compiles, mixin("F()") ) );//true
	mixin( "F();" ); //compiles
	
	pragma(msg, __traits( compiles, mixin("T();") ) ); //false
	pragma(msg, __traits( compiles, mixin("T()") ) ); // true
	mixin( "T();" ); // Error: `structliteral` has no effect in 
expression `T()`
}