Re: [lambda] Latest experimental polymorphic lambda patches

[Jason Merrill <jason at redhat dot com>]

A few comments:

> /* XXX: Any way to get current location? */

input_location

> The following examples produce
> equivalent functions:
>
>    1.   [] (auto x, auto& y, auto const& z) { return x + y + z; }
>    2.   [] <typename X, typename Y, typename Z> (X x, Y& y, Z const& z) { return x + y + z; }
>    3.   [] <typename Y> (auto x, Y& y, auto const& z) { return x + y + z; }

IMO #3 should not be equivalent to the others; the auto template parms 
should come after Y.  And I believe that's currently the case with your 
patch.

> In fact it would be better
> +         to keep building a tree list and only flatten into
> +         a vector after parsing the parameter list. */

If you save up all the auto parms until the end and then assign indices 
and adjust the parm vector then, that will avoid reallocating the vector 
each time.

But don't worry about tidying tree_node_counts; it just tracks how many 
of a particular tree code we create, not how many we currently have. 
Normal GC throws away lots of stuff without adjusting the counts.

> +  /* XXX: Maybe to loop rather than recurse here? */

At -O2, the GCC optimizers should convert tail recursion into looping.

> +  if (type_dependent_expression_p (expr))
> +    /* TODO: Should defer this until instantiation rather than using
> +             decltype.  */
> +    return_type = type_decays_to (non_reference (finish_decltype_type
> +                  (expr, /*id_expression_or_member_access_p=*/false)));

Definitely need to defer it; type_decays_to and non_reference don't work 
on DECLTYPE_TYPE.

Jason