On 21 April 2013 06:51, Timon Gehr <timon.g...@gmx.ch> wrote: > On 04/20/2013 05:56 PM, Dicebot wrote: > >> You miss quite an important point - DIP36 does not add new feature. It >> partially defines existing feature (scope) to replace an existing but >> broken solution (auto ref). Nothing new is really added to the language, >> only existing stuff better defined. >> > > _New meaning_ is assigned to existing grammar whose original purpose is at > most loosely related to the _new_ features. > > I do not think that making 'scope' indicate an rvalue reference is > particularly future proof. >
That's not what scope does. Scope promises that the variables will not escape the scope. And as such, just happens to make passing a temporary by ref safe. It does not implement r-value ref's. It simply allows refs to temporaries to be considered a safe operation. This DIP is actually likely to solve an important source of problems, consider: void func(const ref matrix m); func(x.getMatrix()); // compile error! // fu*^&%$ing hell! you piece of &%^#≈¿$! // ... matrix temp = x.getMatrix(); func(temp); // no more compile error! (but equally unsafe/dangerous) In this example, the 'solution', which is what everybody does right now, is exactly as unsafe as the attempted call with the r-value. ref, as in the language right now, is a fundamentally unsafe operation... and not only is it technically unsafe, a programmer can't even know if it is practically unsafe or not. Since they have a habit of using this hack, they may unknowingly use it in a call site where it's not *practically* safe to do it. They can't know, and by habit (and frustration) they're trained to use this hack everywhere. With 'scope ref' (or 'in ref'), the programmer now has a guide to say whether it's safe to pass a temporary or not. In the future, if the function does not receive scope ref, perhaps the programmer will start to presume that it is NOT safe to pass a temporary, and stop doing so via the current local-variable hack. scope was always intended to implement this promise as far as I'm lead to believe(?). <Side rant> In my experience showing D to new people, this is the #1 complaint. It's the first one that comes up, every time (which really doesn't help with first impressions), and I'm fairly sure every single person I've introduced to D has complained about this. It's kind of embarrassing when I'm saying that D is really cool, and then I have to start making excuses and apologising for this, and assure them that it's a known issue, and it'll be fixed one day.
