Re: [C++0x patch] implement range-based for loops

[Jason Merrill <jason at redhat dot com>]

On 08/23/2010 07:22 AM, Rodrigo Rivas wrote:
> With templates it crashes badly. I've been working on it without success (yet),
> but I've added a temporary warning.
> My problem was that the koenig lookup of the "begin" function does not
> work if the argument is a template dependent name. It would be nice to be able to do:
>      begin = create_temporary_var (make_auto ());
> But that does not work.
> Anyway, that would be wrong because the behavior should be different
> if the range is an array, and we don't know that until instantiation.
> I'd bet that I need to modify the "tsubst_expr()" function, but any
> hint is welcome.

Right.  In a template, rather than call cp_finish_range_based_for, you 
should just build up a RANGE_FOR_STMT with the decl and expr as 
operands; then in tsubst_expr you handle RANGE_FOR_STMT by substituting 
the template arguments into those operands as appropriate and calling 
cp_finish_range_based_for then.

You probably also want to refactor the code a bit so that for a 
range-based for you don't pass the FOR_STMT into 
cp_finish_range_based_for, you call begin_for_stmt inside that function.

Jason