Re: cannot cast

[Namespace]

On Saturday, 28 April 2012 at 14:21:32 UTC, Namespace wrote:
I finished my Ref/NotNull struct, but i've got a problem:
If i try to cast the class, which should implicit convert to 
Ref!(Type) with alias this, i get the following error message:
"cannot cast a1.getRef("Ref.d",72u) of type Ref!(A) to type 
RefTest.Ref.__unittest1.B"

Can someone explain that to me or help me with it?
It seems that alias this replacement isn't smart enough to 
distinguish, if it has to convert.

[code]
import std.conv : to;

struct Ref(T : Object) {
private:
         T _obj;

public:
        @disable
        this();// { }

        @disable
        this(typeof(null));// { }

        this(T obj) {
                assert(obj !is null, "Object is null!");

                this._obj = obj;
        }

        @property
        inout(T) access() inout {
                assert(this._obj !is null, "Access: Object is null!");

                return this._obj;
        }

	//alias access this; // print "Stackoverflow" or "recursive 
expansion"
}

mixin template TRef(T : Object) {
	final Ref!(T) getRef(string file = __FILE__, size_t line = 
__LINE__) in {
		assert(this !is null, "Object is null! @ " ~ file ~ " in Line 
" ~ to!(string)(line) ~ ".");
        } body {
                return Ref!(T)(this);
        }
        
	final Ref!(const T) getRef(string file = __FILE__, size_t line 
= __LINE__) const in {
		assert(this !is null, "Object is null! @ " ~ file ~ " in Line 
" ~ to!(string)(line) ~ ".");
        } body {
                return Ref!(const T)(this);
        }

        alias getRef this;
}

unittest {

        class A {
                mixin TRef!(A);
        }

        class B : A { }

        class C : B { }

        A a1 = new B();
        A a2 = new C();

        B b1 = cast(B) a1; // line 72
}

Trying to fix it with an opCast in Ref ended in an infinity 
loop...