bsl::is_empty

Synopsis

Declared in <bslmf_isempty.h>

template<class t_TYPE>
struct is_empty
    : bsl::integral_constant<bool, ::std::is_empty<t_TYPE>::value>

Description

This struct is a meta-function to determine whether the (template parameter) t_TYPE is an empty class type. This struct derives from bsl::true_type if the t_TYPE is empty, and from bsl::false_type otherwise. This meta-function has the same syntax as the is_empty meta-function defined in the C++11 standard [meta.unary.prop]; on C++03 platforms, however, this meta-function defaults to true_type if t_TYPE is a class or struct with no non-static data members other than bit-fields of length 0, no virtual member functions, no virtual base classes, and no base class B for which is_empty<B>::value is false; otherwise is_empty defaults to false_type. Note that this meta-function will fail to compile for a union that is the same size as an empty class in C++03.

Base Classes

Name	Description
`bsl::integral_constant<bool, ::std::is_empty<t_TYPE>::value>`	Metafunction representing a compile-time constant of the specified (template parameter) `t_TYPE` with the specified (template parameter) `t_VALUE`.

Type Aliases

Name	Description
`type`	Alias for this `integral_constant` specialization.
`value_type`	Alias for the (template parameter) `t_TYPE`.

Member Functions

Name	Description
`operator()`	Return a copy of the template argument `t_VALUE`.
`operator t_TYPE`	Return a copy of the template argument `t_VALUE`.

Static Data Members

Name	Description
`value`	The compile-time constant value of this metafunction.

Derived Classes

Name	Description
`AllocatorTraits_IsAlwaysEqual<ALLOC, false>`	Sets `is_always_equal` to `bsl::is_empty<ALLOC>` when not defined by `ALLOC`.