Alias this incorrectly invoked in conversion to ref

[dlangBugzillaToGithub]

RazvanN (@RazvanN7) reported this on 2018-07-26T11:20:08Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=19117

CC List

• Simen Kjaeraas

Description

struct A
{
    immutable(A) fun() { return  immutable A(); }
    ref A fun2(ref A a)  { return this; }                                                                                                          

    alias fun this;    // line 6
}

void main()
{
    A a, b;
    b.fun2(a);
}

aliasthisbug.d(12): Error: function aliasthisbug.A.fun2(ref A a) is not callable using argument types (A)
aliasthisbug.d(12):        cannot pass argument a of type A to parameter ref A a

Comment line 6 an the error disappears.

[dlangBugzillaToGithub]

razvan.nitu1305 commented on 2018-07-26T11:22:28Z

(In reply to RazvanN from comment #0)
> struct A
> {
>     immutable(A) fun() { return  immutable A(); }
>     ref A fun2(ref A a)  { return this; }                                   
> 
> 
>     alias fun this;    // line 6
> }
> 
> void main()
> {
>     A a, b;
>     b.fun2(a);
> }
> 
> aliasthisbug.d(12): Error: function aliasthisbug.A.fun2(ref A a) is not
> callable using argument types (A)
> aliasthisbug.d(12):        cannot pass argument a of type A to parameter ref
> A a
> 
> Comment line 6 an the error disappears.

Also, changing the signature of fun2 to : ref A fun2(A a) makes the example compile

[dlangBugzillaToGithub]

simen.kjaras commented on 2018-07-26T12:07:09Z

Further simplified:

struct A {
    const(A) fun();
    alias fun this;
}

void fun2(ref A a);

unittest {
    A a;
    fun2(a);
}

This bug triggers when the alias this type is a qualified version of A (shared, const, or immutable), and A has no aliasing (pointers, dynamic arrays, AAs).