[Issue 11857] `out` parameter breaks overload resolution

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=11857



--- Comment #4 from Kenji Hara <k.hara.pg at gmail.com> 2014-01-13 01:09:04 PST ---
(In reply to comment #3)
> So do I understand correctly ICE part of the issue is considered a duplicate of
> issue 11822 and "This code should compile" part is considered WONTFIX? If so,
> where is the documentation claiming such code incorrect?

In short, yes.

Even `const int n = 1` is interpreted in compile time, `n` is a local variable
that has runtime storage on stack. Therefore, expression `n` makes lvalue, then
preferentially matches to `out` parameter.


This behavior is intended to reduce confusion at the situation that mixing
constant-folding and compile-time/runtime evaluation. Example:

void f(    immutable int n);
void f(ref immutable int n);  // accepts only lvalue

void foo(int x)
{
    immutable int n = x;
            // n is evaluated in runtime (when foo is called)
    f(n);   // n matches to ref version
}
void bar(int x)
{
    immutable int n = 1;
            // n can be interpreted at compile time,
            // but still allocated on stack and initialized in runtime.
    f(n);   // n still matches to ref version
}

D is designed to provide consistent overload resolution result for f(n) in both
foo and bar.
In other words, variable evaluation and its ref-ness is strictly separated from
the CTFE/constant-folding. Conflating them would make hard to understand
overload resolution result.

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