[Issue 10574] "auto ref" fails to match when IFTI succeeds (strip to level const)

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=10574



--- Comment #4 from monarchdodra at gmail.com 2013-07-09 03:56:35 PDT ---
(In reply to comment #3)
> (In reply to comment #2)
> > Just an educated guess. The problem seems to be that the value is a L-value so
> > the  signature becomes (ref T[]) which cannot match immutable(int[]).
> 
> That's exactly the current compiler's behavior. "auto ref"  always behave as
> "ref" parameter against lvalue argument `i`, then T[] cannot deduce type T from
> immutable(int[]).

More generally, it seems auto ref will never operate a cast on an lvalue *even
if* the parameter is not templatized. This is strange because auto ref *will*
do it for RValues. Here is another (reduced) example that shows it.

//----
void foo()(auto ref long a);
void main()
{
    int get();
    int a;
    foo(get()); //Fine, rvalue int is cast to long
    foo(a);     //Nope!
}
//----
main.d(7): Error: template main.foo does not match any function template
declaration. Candidates are:
main.d(1):        main.foo()(auto ref long a)
main.d(7): Error: template main.foo()(auto ref long a) cannot deduce template
function from argument types !()(int)
//----



I also spotted this (which, IMO, is even more problematic): 

//----
struct S
{
    @property long get();
    alias get this;
}

void foo()(auto ref long a);
void main()
{
    S s;
    foo(S()); //Fine.
    foo(s);   //Nope!
}
//----

This time, it gives the "cryptic" error:
main.d(14): Error: s.get() is not an lvalue
=> But that's strange: foo takes by auto ref... what do I care about lvalue?

Because s is an Lvalue, it would appear the auto ref is "primed" to take by
ref. It then fails when an actual Rvalue is given.

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