Re: 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");
}