[dmd-beta] ref semantics

[Andrei Alexandrescu]

On 4/12/12 6:40 AM, Michel Fortin wrote:
> Speaking of ref escapes, perhaps it'd be a good time to remind ourselves of this hole:
>
> 	ref int foo(ref int i)
> 	{
> 		return i;
> 	}
>
> 	ref int bar()
> 	{
> 		int i;
> 		return foo(i);
> 	}
>
> 	void main()
> 	{
> 		bar() += 1; // what are we incrementing again?
> 	}
>
> The way ref will work now makes makes it possible to define bar like this instead, which would result in the same generated code:
>
> 	ref int bar()
> 	{
> 		return foo(1);
> 	}
>
> Now the problem is a little more hidden from sight.
>
> I don't see that as a problem of the new ref behaviour (which I like), but since we're looking at ref semantics I thought it'd be good to have a reminder that there's still an important hole related to ref in need of some attention.
>
> <http://d.puremagic.com/issues/show_bug.cgi?id=3925>

I hate this problem. It makes the necessary analysis quite a bit more 
complicated and less precise. Essentially most functions that take a ref 
to a local and return a ref must be analyzed for the possibility they 
return the argument.

Let me look over Kenji's proposal, hopefully it takes care of this 
automatically :o).

Andrei