std::is_placeholder - Man Page

typedef integral_constant< int, __v > type
typedef int value_type

constexpr operator value_type () const noexcept
constexpr value_type operator() () const noexcept

static constexpr int value

struct std::is_placeholder< _Tp >" Determines if the given type _Tp is a placeholder in a bind() expression and, if so, which placeholder it is.

C++11 [func.bind.isplace].

Since

C++11

Definition at line 263 of file functional.