[Issue 19299] string mixins and template mixins should be allowed in function parameter list

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19299

Nick Treleaven <nick at geany.org> changed:

           What    |Removed                     |Added
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                 CC|                            |nick at geany.org

--- Comment #1 from Nick Treleaven <nick at geany.org> ---
Just to mention, you can copy parameters like this:

```d
// simpler version of std.traits.Parameters (which also works)
template Params(alias func)
{
    static if (is(typeof(func) PS == __parameters))
        alias Params = PS;
}

void f(Params!g, int extra);
void g(char c = 0, byte b);

pragma(msg, typeof(f));
```

If you need just one parameter, use slicing `PS[i..i+1]` rather than indexing
and it will preserve not just the type but the identifier and default argument
too.

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