bslmf_ispair

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).