IntrusivePtr.opCastImpl

static struct Foo{
    ControlBlock!(int, int) c;
    int i;
    alias i this;

    this(int i)pure nothrow @safe @nogc{
        this.i = i;
    }
}

import std.conv;

IntrusivePtr!Foo x = IntrusivePtr!Foo.make(123);
assert(x.useCount == 1
);
auto y = cast(IntrusivePtr!(const Foo))x;
//debug assert(x.useCount == 2, x.useCount.to!string);
assert(x.useCount == 2);


auto z = cast(const IntrusivePtr!Foo)x;
assert(x.useCount == 3);

auto u = cast(const IntrusivePtr!(const Foo))x;
assert(x.useCount == 4);