CODEWITHSUNDEEP
c++c++20
Alexey Starinsky
Alexey Starinsky

Reputation: 4305

How to check if a class have a specific constructor?

I have the following source code:

std::string s;
std::string_view sv(s.begin(), s.end());

that compiles with MSVC and GCC, but does not compile with Apple Clang.

What is the right way to write a function like

template< class It >
constexpr std::string_view make_string_view( It first, It last );

that would compile with both C++17 and C++20 and use new std::string_view constructor accepting two iterators if possible?

Upvotes: 2

Views: 105

Answers (1)

tomaszmi
tomaszmi

Reputation: 520

You would need to check at compile time that:

  1. Iterators are of random access
  2. Their value_type is std::string_view::value_type

You may check by using the std::iterator_traits class, std::is_same_v type trait and static_assert. Having that done you could calculate the distance from first to last (by using std::distance) and call the following std::string_view constructor:

constexpr basic_string_view( const CharT* s, size_type count );

For s, you could pass std::addressof(*first), and for the count the result of the std::distance call.

Upvotes: 5

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