[func.bind.place] (original) (raw)

22 General utilities library [utilities]

22.10 Function objects [function.objects]

22.10.15 Function object binders [func.bind]

22.10.15.5 Placeholders [func.bind.place]

namespace std::placeholders { see below _1;see below _2; ⋮see below _ M;}

The number M of placeholders isimplementation-defined.

All placeholder types meet the Cpp17DefaultConstructible andCpp17CopyConstructible requirements, and their default constructors and copy/move constructors are constexpr functions that do not throw exceptions.

It is implementation-defined whether placeholder types meet the Cpp17CopyAssignable requirements, but if so, their copy assignment operators are constexpr functions that do not throw exceptions.

Placeholders should be defined as:inline constexpr unspecified _1{};

If they are not, they are declared as:extern unspecified _1;