std:: is_literal_type

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is_literal_type
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Defined in header <type_traits>
template < class T >
struct is_literal_type ;
(since C++11)
(deprecated in C++17)
(removed in C++20)

std::is_literal_type is a UnaryTypeTrait .

(This type trait has been deprecated [1] and removed [2] as offering negligible value to generic code.)

If T satisfies all requirements of LiteralType , provides the member constant value equal to true . For any other type, value is false .

If std:: remove_all_extents_t < T > is an incomplete type and not (possibly cv-qualified) void , the behavior is undefined.

If the program adds specializations for std::is_literal_type or std::is_literal_type_v , the behavior is undefined.

Template parameters

T - a type to check

Helper variable template

template < class T >
constexpr bool is_literal_type_v = is_literal_type < T > :: value ;
(since C++17)
(deprecated)
(removed in C++20)

Inherited from std:: integral_constant

Member constants

value
[static]
true if T is a literal type, false otherwise
(public static member constant)

Member functions

operator bool
converts the object to bool , returns value
(public member function)
operator()
(C++14)
returns value
(public member function)

Member types

Type Definition
value_type bool
type std:: integral_constant < bool , value >

Notes

Only literal types may be used as parameters to or returned from constexpr functions . Only literal classes may have constexpr member functions.

Example

Run this code 
#include <type_traits>
 
struct A { int m; };
static_assert(std::is_literal_type_v<A> == true);
 
struct B { virtual ~B(); };
static_assert(std::is_literal_type_v<B> == false);
 
int main() {}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2015 C++11 T could be an array of incomplete
class type with unknown bound 		the behavior is
undefined in this case

External links

  1. ↑ Alisdair Meredith. "Deprecate the is_literal Trait" . Deprecating Vestigial Library Parts in C++17 . "The is_literal type trait offers negligible value to generic code, as what is really needed is the ability to know that a specific construction would produce constant initialization."
  2. ↑ Alisdair Meredith, Stephan T. Lavavej, Tomasz Kamiński. "Deprecated type traits" . Reviewing Deprecated Facilities of C++17 for C++20 . " Strong recommendation: Remove the traits that can live on as zombies. [...] Toronto Review: Accept strong recommendation, strike from C++20."
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