gdbsupport: make filtered_iterator work with pointers
It's currently not possible to use filtered_iterator with a pointer as
the base iterator type. This patch makes it possible. The indended
usage is:
Foo array[12];
Foo *begin = array;
Foo *end = array + ARRAY_SIZE (array);
filtered_iterator<Foo *, FooFilter> (begin, end);
Here are the things that needed changing:
- Give filtered_iterator a constructor where the caller provides
already constructed begin and end iterators. filtered_iterator
currently assumes that default-constructing a BaseIterator will
produce a valid "end" iterator. This is not the case if BaseIterator
is a pointer. The caller needs to pass in the end of the array /
region to iterate on as the end.
- Typedefs of member types like wouldn't work:
typedef typename BaseIterator::value_type value_type;
The compiler would complain that it's not possible to apply `::` to
type `BaseIterator` (aka `Foo *`). Use std::iterator_traits to fix
it [1].
- Similarly, the compiler would complain about the use of
`BaseIterator::operator*` in the return type of
`filtered_iterator::operator*`. Fix this by using `decltype(auto)`
as the return type. This lets the compiler deduce the return type
from the return statement. Unlike `auto`, `decltype(auto)` perfectly
preserves the "cvref-ness" of the deduced return type. If the return
expression yields a `Foo &`, then the function will return a `Foo &`
(which is what we want), whereas it would return a `Foo` if we used
just `auto`.
Improve the filtered_iterator unit tests to run the same tests but with
pointers as iterators. Because the filtered_iterator objects are
initialized differently in the two scenarios, I chose to copy the
existing code and adapt it. It would probably be possible to add a
layer of abstraction to avoid code duplication, but it would end up more
complicated and messy. If we ever add a third scenario, we can revisit
that.
[1] https://en.cppreference.com/w/cpp/iterator/iterator_traits.html
Change-Id: Id962ffbcd960a705a82bc5eb4808b4fe118a2761
Approved-By: Tom Tromey <tom@tromey.com>
2 files changed
