DIP44: scope(class) and scope(struct)

[H. S. Teoh]

On Sat, Aug 24, 2013 at 11:30:26PM -0700, Walter Bright wrote:
[...]
> Your example, again, is of an auto-generated dtor. But you said
> earlier that wasn't the point.
> 
> Without the auto-generated dtor, it is just scope(failure), which is
> already a D feature.
> 
> I don't get it.

It's a way to avoid code duplication in the dtor. If you just had
scope(failure), you have to factor out a __cleanup method in order to do
cleanup on both a failed ctor call or a dtor call, as I did in the
example.

I don't know if it will clarify things, but if you already have a dtor,
then scope(this) just adds to it:

	class C {
		this() {
			scope(this) writeln("A");
			scope(this) writeln("B");
		}
		~this() {
			writeln("In dtor");
		}
	}

This would get lowered to the equivalent of:

	class C {
		this() {
			scope(failure) __cleanup();
			__cleanups ~= { writeln("A"); };
			__cleanups ~= { writeln("B"); };
		}

		void delegate()[] __cleanups;

		void __cleanup() {
			foreach_reverse (f; __cleanups)
				f();
		}

		~this() {
			writeln("In dtor");
			__cleanup();
		}
	}


T

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