Re: Adding optional<T&> find like method to associative containers in boost.

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2024-12-18 09:33:38

On 12/18/24 12:12, Ivan Matek via Boost wrote:
> 
> Existing Practice
> We have
> std::basic_string<CharT,Traits,Allocator>::starts_with
> std::basic_string_view<CharT,Traits>::starts_with
> although there is(or more precisely there will be)
> std::ranges::starts_with
> 
> You may say that having member function 2 times is fine since it duplicated
> just 2 times, but we also have
> 
> std::set<Key,Compare,Allocator>::contains
> std::map<Key,T,Compare,Allocator>::contains
> std::unordered_set<Key,Hash,KeyEqual,Allocator>::contains
> std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::contains
> std::multiset<Key,Compare,Allocator>::contains
> std::multimap<Key,T,Compare,Allocator>::contains
> std::unordered_multiset<Key,Hash,KeyEqual,Allocator>::contains
> std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::contains
> 
> If you say this is just some modern C++ nonsense:
> Since C++98 containers had empty member function although it is trivially
> implementable with free function empty. Here not even talking about
> "complicated" C++17 std::empty that understands C arrays/std::array/...,
> talking about simple function that could just take container with size
> member function.
> template<typename C>
> bool empty(const C& c) { return c.size() == 0; }
> 
> But for decades we have this duplication in member functions since empty is
> commonly called function.

std::list::size() had linear complexity in C++03 and std::list::empty()
was constant. It was definitely a reason to have it separate from size().

contains() is a specialized algorithm that is not equivalent to
`std::find() != end()` in each container's case. Historically, such
specialized algorithms were implemented as members, while the generic
algorithms were provided as free functions. Another such example is swap().

std::string is probably a bad example to mention in favor of member
functions as it is generally agreed that it has a bloated interface.