[Issue 3925] Missed escaping reference of a local variable

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http://d.puremagic.com/issues/show_bug.cgi?id=3925


Don <clugdbug at yahoo.com.au> changed:

           What    |Removed                     |Added
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                 CC|                            |clugdbug at yahoo.com.au


--- Comment #2 from Don <clugdbug at yahoo.com.au> 2010-03-10 11:12:03 PST ---
(In reply to comment #1)
> This was the original code by Michel Fortin:
> 
> @safe ref int foo(ref int a) {
>     return a;
> }
> @safe ref int bar() {
>     int a;
>     return foo(a);
> }
> 
> 
> Norbert Nemec comments:
> >I would say the possibility of a bug makes this code unsafe by definition. Ref returns must be considered unsafe by default, unless the compiler can know for sure that the object will exist beyond the lifetime of the function.<
> 
> 
> So I think Norbert Nemec idea is: while the normal compiler error messages
> assume correctness and need a demonstration of unsafety to be shown, @safe can
> do the opposite assuming unsafety and requiring a demonstration of safety.

I've just been dealing with ref returns in my recent CTFE patch. But I don't
think it's very complicated.
As far as I can tell, ref returns are only a problem if a local variable is
passed as a ref parameter, or if it is a member function of a local struct.
If either of those is true, it should be considered to potentially be a return
of a local variable.
I don't think there's any problem with foo, but bar should generate an error.

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