bslalg_hastrait

Macros
#define	bslalg_HasTrait   bslalg::HasTrait
	This alias is defined for backward compatibility.

Detailed Description

Outline

• Purpose
• Classes
• Description
  • Usage

Purpose

Provide a meta-function to detect if a type has a given trait.

Deprecated:

Do not use.

Classes

• bslalg::HasTrait: legacy mechanism for detecting type traits

See also

bslalg_typetraits, bslmf_integralconstant

Description

This component provides a meta-function, bslalg::HasTrait, that is a legacy mechanism for detecting traits. bslalg::HasTrait takes two template parameters, TYPE and TRAIT. bslalg::HasTrait<TYPE, TRAIT> inherits from bsl::true_type if the (template parameter) TYPE has the (template parameter) TRAIT, and inherits from bsl::false_type otherwise.

bslalg::HasTrait is not a general-purpose trait detection facility. It is intended to be used in conjunction with the legacy (deprecated) bslalg traits only. In particular, the type supplied to bslalg::HasTrait as the TRAIT template parameter must be a bslalg trait, for example, bslalg::TypeTraitUsesBslmaAllocator. Supplying anything else for TRAIT will (more than likely) fail to compile. For example, the following errant use of bslalg::HasTrait will definitely fail to compile:

bslalg::HasTrait<Foo, bsl::is_trivially_default_constructible>'

See bslalg_typetraits for a complete list of the bslalg traits that are supported by bslalg::HasTrait.

In lieu of the deprecated bslalg traits, the newer traits intended to replace them should be used instead. These successor traits are typically defined in bslmf (two exceptions are bslma::UsesBslmaAllocator and bslalg::HasStlIterators). bslalg::HasTrait and the bslalg traits that it supports are written in such a way that bslalg::HasTrait will correctly detect whether a type has a given trait regardless of whether the trait is ascribed to the type using the deprecated BSLALG_DECLARE_NESTED_TRAITS* or BSLMF_NESTED_TRAIT_DECLARATION macros (see bslalg_typetraits and bslmf_nestedtraitdeclaration , respectively), or whether the (preferred) C++11 idiom for defining traits is used (see bslmf_detectnestedtrait ). In this way, bslalg::HasTrait provides a "bridge" between legacy bslalg type traits and their replacements that facilitates the migration to the newer traits.

Usage

No Usage example is provided since this component is deprecated.

Macro Definition Documentation

bslalg_HasTrait

#define bslalg_HasTrait   bslalg::HasTrait