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digitalmars.D.learn - UDA and ReturnType!(__traits...) doesn't work

reply "filcuc" <filippocucchetto gmail.com> writes:
Hi all,
i'm working in the generation of the code but i'm failing in 
extracting a function return type when invoking the 
ReturnType!(T) type trait and mixing it with __traits(getMember) 
function.
Can anyone help me? or explaining what is happenning?
i've created a gist here: 
https://gist.github.com/filcuc/14c3a6cac89beb69cccd

The error message is the following:

main.d-mixin-58(58): Error: template instance 
main.Person.ReturnType!(name) does not match template declaration 
ReturnType(func...) if (func.length == 1 && isCallable!func)
main.d-mixin-58(58): Error: template instance 
std.traits.ReturnType!(Monitor) does not match template 
declaration ReturnType(func...) if (func.length == 1 && 
isCallable!func)
main.d(73): Error: template instance main.IterateUDA!(Person) 
error instantiating
May 03 2015
next sibling parent "Meta" <jared771 gmail.com> writes:
On Sunday, 3 May 2015 at 17:22:00 UTC, filcuc wrote:

 Hi all,
 i'm working in the generation of the code but i'm failing in 
 extracting a function return type when invoking the 
 ReturnType!(T) type trait and mixing it with 
 __traits(getMember) function.
 Can anyone help me? or explaining what is happenning?
 i've created a gist here: 
 https://gist.github.com/filcuc/14c3a6cac89beb69cccd

 The error message is the following:

 main.d-mixin-58(58): Error: template instance 
 main.Person.ReturnType!(name) does not match template 
 declaration ReturnType(func...) if (func.length == 1 && 
 isCallable!func)
 main.d-mixin-58(58): Error: template instance 
 std.traits.ReturnType!(Monitor) does not match template 
 declaration ReturnType(func...) if (func.length == 1 && 
 isCallable!func)
 main.d(73): Error: template instance main.IterateUDA!(Person) 
 error instantiating


Try adding the following around your 'string returnType = ...' 
code:

static if(isSomeFunction!(__traits(get member, T, member))
{
     ...
}

The problem is that you're looping over all the fields in T, 
including the data members which obviously don't have a return 
type. I guess ReturnType should probably use a static assert to 
give a better error message.
May 03 2015
prev sibling parent reply ketmar <ketmar ketmar.no-ip.org> writes:
On Sun, 03 May 2015 17:21:58 +0000, filcuc wrote:


 Hi all,
 i'm working in the generation of the code but i'm failing in extracting
 a function return type when invoking the ReturnType!(T) type trait and
 mixing it with __traits(getMember) function.
 Can anyone help me? or explaining what is happenning?
 i've created a gist here:
 https://gist.github.com/filcuc/14c3a6cac89beb69cccd
=20
 The error message is the following:
=20
 main.d-mixin-58(58): Error: template instance
 main.Person.ReturnType!(name) does not match template declaration
 ReturnType(func...) if (func.length =3D=3D 1 && isCallable!func)
 main.d-mixin-58(58): Error: template instance
 std.traits.ReturnType!(Monitor) does not match template declaration
 ReturnType(func...) if (func.length =3D=3D 1 && isCallable!func)
 main.d(73): Error: template instance main.IterateUDA!(Person) error
 instantiating


the thing is that you mixed CTFE and runtime code in a weird way. ;-)

the following works:

void IterateUDA(T)() {
  import std.typetuple : staticIndexOf;
  foreach (member; __traits(allMembers, T)) {
    // Check that the given member is a function
    static if (is(typeof(__traits(getMember, T, member)))) {
      bool isFunction =3D __traits(isVirtualFunction, __traits(getMember,=20
T, member));
      if (!isFunction) continue;
      // Retrieve the UDA
      enum attributes =3D __traits(getAttributes, __traits(getMember, T,=20
member));
      // Extract the Function Return Type and Arguments if `Slot()` is=20
found
      static if (staticIndexOf!(Slot(), attributes) >=3D 0) {
        enum returnType =3D ReturnType!(__traits(getMember, T,=20
member)).stringof;
        import std.stdio;
        writeln(returnType);
      }
    }
  }
}

yet i think you need to read more about CTFE and metaprogramming, to=20
avoid mixing different code.=
May 03 2015
parent reply "filcuc" <filippocucchetto gmail.com> writes:
On Sunday, 3 May 2015 at 17:48:55 UTC, ketmar wrote:

 On Sun, 03 May 2015 17:21:58 +0000, filcuc wrote:


 Hi all,
 i'm working in the generation of the code but i'm failing in 
 extracting
 a function return type when invoking the ReturnType!(T) type 
 trait and
 mixing it with __traits(getMember) function.
 Can anyone help me? or explaining what is happenning?
 i've created a gist here:
 https://gist.github.com/filcuc/14c3a6cac89beb69cccd
 
 The error message is the following:
 
 main.d-mixin-58(58): Error: template instance
 main.Person.ReturnType!(name) does not match template 
 declaration
 ReturnType(func...) if (func.length == 1 && isCallable!func)
 main.d-mixin-58(58): Error: template instance
 std.traits.ReturnType!(Monitor) does not match template 
 declaration
 ReturnType(func...) if (func.length == 1 && isCallable!func)
 main.d(73): Error: template instance main.IterateUDA!(Person) 
 error
 instantiating


 the thing is that you mixed CTFE and runtime code in a weird 
 way. ;-)

 the following works:

 void IterateUDA(T)() {
   import std.typetuple : staticIndexOf;
   foreach (member; __traits(allMembers, T)) {
     // Check that the given member is a function
     static if (is(typeof(__traits(getMember, T, member)))) {
       bool isFunction = __traits(isVirtualFunction, 
 __traits(getMember,
 T, member));
       if (!isFunction) continue;
       // Retrieve the UDA
       enum attributes = __traits(getAttributes, 
 __traits(getMember, T,
 member));
       // Extract the Function Return Type and Arguments if 
 `Slot()` is
 found
       static if (staticIndexOf!(Slot(), attributes) >= 0) {
         enum returnType = ReturnType!(__traits(getMember, T,
 member)).stringof;
         import std.stdio;
         writeln(returnType);
       }
     }
   }
 }

 yet i think you need to read more about CTFE and 
 metaprogramming, to
 avoid mixing different code.



Yep sorry,
i'm still learning :)

However thank you all for your help and the quick answer.

As you suggested wrapping the body with the static if solved the 
problem.
I've updated the gist
https://gist.github.com/filcuc/14c3a6cac89beb69cccd

Thanks!
May 03 2015
parent ketmar <ketmar ketmar.no-ip.org> writes:
On Sun, 03 May 2015 18:02:37 +0000, filcuc wrote:


 Yep sorry,
 i'm still learning :)


i'm not blaming you at all. what i mean i that i'm bad at explanations,=20
so you'd better read one of the D books to better understand my cryptic=20
"don't do that, do this" comments. ;-)=
May 03 2015