[Issue 24717] alias edge cases with tupleof

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24717

Nick Treleaven <nick at geany.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|critical                    |enhancement

--- Comment #4 from Nick Treleaven <nick at geany.org> ---
> alias y = s.tupleof[0]; // this is a compile error?!

The error is:
Error: alias `y` cannot alias an expression `AliasSeq!(s.x)[0]`

That is because an alias declaration cannot target a value.

For:
struct S {
    int x;
    alias expand=Seq!x;
}

Turns out .tupleof is actually equivalent to the `expand` alias, see:
https://forum.dlang.org/post/vaue5d$1quo$1@digitalmars.com

    alias z = AliasSeq!(s.tupleof);
    z[0].writeln(); // Error: accessing non-static variable `x` requires an
instance of `S`

So the above error is consistent with the design of symbol aliases. Changing
this issue to an enhancement.

--