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

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.

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.

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!

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, so you'd better read one of the D books to better understand my cryptic "don't do that, do this" comments. ;-)