How to check that function gets ref parameter?

[Basile B.]

On Sunday, 13 December 2020 at 16:41:06 UTC, Andrey Zherikov 
wrote:
> I'm trying to check that function has 'ref' parameter. The only 
> way I found so far is to use std.traits.Parameters.
>
> Here is the code I have:
>     void f(int) {}
>     void g(ref int) {}
>     void main()
>     {
>         writeln(Parameters!f[0].stringof);
>         writeln(__traits(isRef, Parameters!f[0]));
>         writeln(Parameters!g.stringof);
>         writeln(Parameters!g[0].stringof);
>         writeln(__traits(isRef, Parameters!g[0]));
>     }
>
> The output is:
>     int
>     false
>     (ref int)
>     int
>     false
>
> "Parameters!g[0]" strips off 'ref' qualifier as you can see. 
> How can I make it work?

You use the wrong traits, try ParameterStorageClassTuple instead:

   void f(int) {}
   void g(ref int) {}
   import std.traits : ParameterStorageClass, 
ParameterStorageClassTuple;
   static assert(ParameterStorageClassTuple!g[0] == 
ParameterStorageClass.ref_);
   static assert(ParameterStorageClassTuple!f[0] != 
ParameterStorageClass.ref_);