Bug 8762 – instanceOf trait for static conditionals

As discussed here: http://forum.dlang.org/thread/[email protected] The idea would be a trait "instanceOf!T" that returns a reference to a T. The advantage of this approach is that it allows "extracting" an instance out of T, without ever worrying about how or where said instance came from. This is particularly important because some types don't have T.init, and immutables don't have T t = void. The intersection of both these groups is {0} ... Example: //---- template isAssignable(T, U) { enum bool isAssignable = is(typeof(instanceOf!T = instanceOf!U)); } //---- The "signature" (as improved on by Simen Kjaeraas) would be: //---- @property ref T instanceOf( T )( ); //---- But remain un-implemented. This would ensure it is not actually usable during run-time.

In std.traits module, similar utility already exists (but today, it is private template). And recently I've posted a pull request which updates it. https://github.com/D-Programming-Language/phobos/pull/842 https://github.com/D-Programming-Language/phobos/pull/842/files#L1R140 The name `defaultInit` comes from `default initializer` for T (, and the name is used in the dmd implementation).

We have lvalueOf/rvalueOf now, is this sufficient?

(In reply to Andrej Mitrovic from comment #2) > We have lvalueOf/rvalueOf now, is this sufficient? Yes. Wow, I posted this a long time ago... Closing as fixed.