Using function from another namespace C++

Question

I want to create aliases for a few of the Range-V3 functions/functors into my own namespace. For the functors like begin, end, it's just doing auto constexpr begin = ::ranges::begin. However, for a function like copy, I'm not sure how to proceed. I've tried using ::ranges::copy(); and using ::ranges::copy; but neither work.

Any help would be much appreciated! A small example of what I'm doing:

namespace example::ranges
{
   auto constexpr begin = ::ranges::begin;
   auto constexpr end = ::ranges::end;
   auto constexpr size = ::ranges::size;
   using ::ranges::copy(); // Doesn't work
}

What is ::ranges::copy? A function, a class, a typedef,... ? Maybe already a using? — Robert Andrzejuk
– Robert Andrzejuk, Commented Oct 4, 2018 at 16:04
Is there a reason why you only want to create "a few" aliases? Otherwise it would be as simple as namespace example { namespace ranges = ::ranges; }. — zett42
– zett42, Commented Oct 4, 2018 at 16:12

Vittorio Romeo · Accepted Answer · 2020-11-06 17:33:38Z

3

Unfortunately there is no straightforward way to create aliases for functions in C++ (yet). Your best bet is creating a perfectly-forwarding wrapper:

namespace example::ranges
{
    template <typename... Ts>
    auto begin(Ts&&... xs)                   
        noexcept(noexcept(::ranges::begin(std::forward<Ts>(xs)...))) 
              -> decltype(::ranges::begin(std::forward<Ts>(xs)...)) {
                   return ::ranges::begin(std::forward<Ts>(xs)...);
    }
}

This will behavely as closely as possible to the original function, retaining its noexcept-ness, SFINAE-friendliness, and overloaded behavior. The triplication can be simplified with a macro.

edited Nov 6, 2020 at 17:33

answered Oct 4, 2018 at 15:53

Vittorio Romeo

94.1k37 gold badges276 silver badges451 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

brrrlinguist Over a year ago

Ahhh I was hoping that wouldn't be the case. What do you mean by "yet"? Is it planned for C++20?

Vittorio Romeo Over a year ago

@brrrlinguist: this was discussed in Rapperswil, but there was no consensus

Arek' Fu Over a year ago

I think the noexcept specifier should appear before the trailing return type. Can you please fix it?

Collectives™ on Stack Overflow

Using function from another namespace C++

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related