Re: alias this doesn't work for properties.

[Adam D. Ruppe]

On Friday, 2 August 2013 at 00:36:19 UTC, JS wrote:
Realize that the ultimate goal is to assign 3 to x?

A working solution is to just use opAssign. I think of alias this 
as being implicit cast to , whereas opAssign is implicit cast 
from (well, sort of, it only works on assignments, but there's 
also constructors you can do. Where it falls short of full 
implicit cast is stuff like function calls)

Anyway, try this:

class A
{
    double x;
    @property double X() { return x; }
    @property double X(double v) { return x = v; }
    alias X this;

    // new
    A opAssign(double rhs) { x = rhs; return this; }
}

Now:

        A a = new A();
        a = 3.14; // ok


Then the next question is b.Y = 3, which is one of those cases 
where it just isn't going to work like that. Y is pretty explicit 
about *wanting* an A, this isn't setting to an A, this would 
actually be implicit construction which is generally a no-no in D.

However, if you add:

    @property A Y(double v) { return a = v; }

to class B, then it will compile, with a = v calling A.opAssign.



A cool thing about opAssign that aias this doesn't do right now 
is it can be templated or you can overload it, and handle a vast 
variety of types.