[Issue 20555] New: Request to add trait matching to __traits(getOverloads, ...) to std.traits library module

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20555

          Issue ID: 20555
           Summary: Request to add trait matching to
                    __traits(getOverloads, ...) to std.traits library
                    module
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: neuranuz at gmail.com

I consider that current way of getting overloads list for symbol is ugly.
Currently using __traits directly (as far as I understand) is considered as
mean of last resort by much of the programmers. And is not a very good
practice.
Let's look how we usually get overloads in some generic code:

void foo(string param1) {}
void foo(string param1, int param2, bool param3) {}

template Bar(alias Func)
{
    alias Bar = __traits(getOverloads, __traits(parent, Func),
__traits(identifier, Func));
}

The problemme is that whan I already have direct alias for symbol I need to do
completelly useless and unnecessary steps to get `parent` of symbol and get
it's identifier. So compiler maybe calculates alias for symbol again which
could be less effective (but it's just assumption) /

I believe that we need a simple way to get overloads with template in
std.traits.
I request the following simple signature:
template GetOverloads(alias symbol)
{
   // whatever
}

The extra question is related to using __trait(getOverloads, ...) with symbols
like lambda functions. Let's consider this example: 

template Bar(alias Func) {
    alias Bar = __traits(getOverloads, __traits(parent, Func),
__traits(identifier, Func));
}

alias Test = Bar!(() { return `test`; }); 

This doesn't compile, because seems that it cannot get access to lamda for some
reason:
//----
onlineapp.d(4): Error: no property __lambda1 for type void
onlineapp.d(4): Error: main().__lambda1 cannot be resolved
onlineapp.d(9): Error: template instance onlineapp.Bar!(function () pure
nothrow @nogc @safe => "test") error instantiating
//----

I know that lambda usually cannot have any overloads, because unique name is
created internally to every lambda. So it just always has 1 overload. But lamda
is still a function, so it's expected that it should be treated the same way as
others. It is not very convenient to write come generic code if I need to do
extra special handling for lambda in this case. Everything should `just work`.
Thanks...

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