Component bslmf_ispair [Package bslmf]

Provide a compile-time check for the bsl::pair type. More...

Namespaces
namespace	bslmf

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Detailed Description

Outline

• Purpose
• Classes
• Description
  • Usage notes

Purpose:

Provide a compile-time check for the bsl::pair type.

Classes:

bslmf::IsPair

meta-function for determining the bsl::pair type.

See also:

Description:

This component defines a simple template structure used to evaluate whether it's parameter is a bsl::pair type. A t_TYPE that has this trait fulfills the following requirements, where mX is a modifiable object and X a non-modifiable object of t_TYPE:

  Valid expression     Type
  ----------------     ----
  t_TYPE::first_type
  t_TYPE::second_type

  mX.first             first_type
  mX.second            second_type
  X.first              const first_type
  X.second             const second_type

Note that first and second are not member functions, but data members.

Usage notes:

The bslmf::IsPair trait is not used to construct pair objects, as a pair behaves like any other type w.r.t. the constructors and bslma::Allocator. Nevertheless, it is used for different purposes in libraries that depend on bslalg. For instance, some libraries use it for printing (a pair does not have a printing method, but it is possible to use the trait to forward the call to print to its two members if they both have the printable trait).