Re: Should boost have ofind(_if), that returns boost::optional<T&>?

From: Marshall Clow (mclow.lists_at_[hidden])
Date: 2022-04-04 02:32:11

On Apr 3, 2022, at 5:01 PM, Gavin Lambert via Boost <boost_at_[hidden]> wrote:
> 
> On 4/04/2022 10:58, Marshall Clow wrote:
>> On Apr 3, 2022, at 3:09 PM, Viktor Sehr wrote:
>>> 
>>> Why not return a pointer/nullptr instead? pfind_if
>> Why not just check to see if the returned iterator == end () ?
> 
> The annoyance with the iterator == end() implementation is that it's a double indirection -- if you want to access the value afterwards it has to be in a separate statement, which means you can't do it with an rvalue collection.
> 
> The same applies with a pointer-find; it's still a non-owning indirection that's invalid on rvalue collections.
> 
> The optional return doesn't have that problem; because it copies the value, the value remains valid when returned from an rvalue collection.

Actually, that’s not what Ivan proposed.
He proposed returning an optional<T&>.

— Marshall