Getting the const-correctness of Object sorted once and for all

[John]

On Monday, 14 May 2012 at 06:04:33 UTC, Mehrdad wrote:
> On Monday, 14 May 2012 at 03:19:57 UTC, Jonathan M Davis wrote:
>> I suspect that the folks who are looking for absolutely every 
>> CPU cycle and want caching and lazy-loading in their types
>
> It's not a CPU cycle issue.
>
> Caching/lazy-loading can make the difference between a window 
> that freezes, and a window that doesn't.

You can still do this pretty easily.  You just have to cast away 
const.

You can even make it reusable.

mixin template TrustedToString() {
    const @safe pure nothrow string toString() {
       return unsafeToString();
    }
    final const @trusted pure nothrow string unsafeToString() {
       auto nonConstThis = cast(Unqual!(typeof(this)))this;
       return nonConstThis.trustedToString();
    }
}

class Foo {
  public:
    const @safe pure nothrow string toString() {
       return "Foo";
    }
}

class Bar : Foo {
  public:
    mixin TrustedToString;
    final pure @trusted nothrow string trustedToString() {
       if (cachedString.length == 0) {
          cachedString = "Bar";
       }
       return cachedString;
    }
    string cachedString;
}

unittest {
    auto f = new Foo();
    assert(f.toString() == "Foo");

    auto b = new Bar();
    assert(b.toString() == "Bar");
}