std::is_literal_type
Defined in header <type_traits> |
||
---|---|---|
template< class T > struct is_literal_type; |
(since C++11) (deprecated in C++17) (removed in C++20) |
(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 true
. For any other type, value
is false
.
The behavior is undefined if std::remove_all_extents_t<T>
is an incomplete type and not (possibly cv-qualified) void
.
The behavior of a program that adds specializations for is_literal_type
or is_literal_type_v
(since C++17) is undefined.
Template parameters
T | - | a type to check |
Helper variable template
template< class T > inline 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
#include <iostream> #include <type_traits> struct A { int m; }; struct B { virtual ~B(); }; int main() { std::cout << std::boolalpha; std::cout << std::is_literal_type<A>::value << '\n'; std::cout << std::is_literal_type<B>::value << '\n'; }
Output:
true false
External links
- Alisdair Meredith. "Deprecate the
is_literal
Trait". Deprecating Vestigial Library Parts in C++17. "Theis_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." - 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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