On 11/13/20 1:13 AM, Richard Sandiford via Gcc-patches wrote:
> This patch adds some more iterator helper classes. They really fall
> into two groups, but there didn't seem much value in separating them:
>
> - A later patch has a class hierarchy of the form:
>
> Base
> +- Derived1
> +- Derived2
>
> A class wants to store an array A1 of Derived1 pointers and an
> array A2 of Derived2 pointers. However, for compactness reasons,
> it was convenient to have a single array of Base pointers,
> with A1 and A2 being slices of this array. This reduces the
> overhead from two pointers and two ints (3 LP64 words) to one
> pointer and two ints (2 LP64 words).
>
> But consumers of the class shouldn't be aware of this: they should
> see A1 as containing Derived1 pointers rather than Base pointers
> and A2 as containing Derived2 pointers rather than Base pointers.
> This patch adds derived_iterator and const_derived_container
> classes to support this use case.
>
> - A later patch also adds various linked lists. This patch adds
> wrapper_iterator and list_iterator classes to make it easier
> to create iterators for these linked lists. For example:
>
> // Iterators for lists of definitions.
> using def_iterator = list_iterator<def_info, &def_info::next_def>;
> using reverse_def_iterator
> = list_iterator<def_info, &def_info::prev_def>;
>
> This in turn makes it possible to use range-based for loops
> on the lists.
>
> The patch just adds the things that the later patches need; it doesn't
> try to make the classes as functionally complete as possible. I think
> we should add extra functionality when needed rather than ahead of time.
>
> gcc/
> * iterator-utils.h (derived_iterator): New class.
> (const_derived_container, wrapper_iterator): Likewise.
> (list_iterator): Likewise.
OK
jeff
