Re: Understanding opAssign and 'alias this'

[Maxim Fomin]

On Monday, 14 October 2013 at 10:45:26 UTC, Maurice wrote:
On Monday, 14 October 2013 at 09:32:15 UTC, Maxim Fomin wrote:
On Monday, 14 October 2013 at 09:17:12 UTC, John Colvin wrote:
Everything is working fine except for the error on [2] when 
xxx == true, which I think is a bug.

minimised test:

struct A
{
      void opAssign(A a) {}
}

struct B {
      A a;
      alias a this;
}

void main() {
      A a;
      B b;
      b = a;
}

Error: function assign.B.opAssign (B p) is not callable using 
argument types (A)

This does not work (and need not) because compiler generates 
default function B.opAssign(B) which is really not callable 
using argument types (A).

Then why does it work when replacing "opAssign(A a)" with 
"opAssign(int)"?

struct A {
        void opAssign(int) {}
}

struct B {
        A a;
        alias a this;
}

void main() {
        A a;
        B b;
        b = a; // This now compiles fine...
}

OK, it seems to be what actually causes the problem is implicit 
conversion from B to A. Situation depends on presence of 
A.opAssign(A ) because when compiler tries to resolve function 
call, it is confused between calling B.opAssign(B) and casting 
through alias this B to A and calling A.opAssign(A). When it 
realizes that there is no best match it throws error. Since 
argument B is casted to A, the error message looks so weird.