Specifies that a type is a literal type. Literal types are the types of constexpr variables and they can be constructed, manipulated, and returned from constexpr functions.
Note, that the standard doesn't define a named requirement or concept with this name. This is a type category defined by the core language. It is included here as concept only for consistency.
Requirements
A literal type is any of the following:
| (since C++14) |
- scalar type;
- reference type;
- an array of literal type;
- possibly cv-qualified (since C++17) class type that has all of the following properties:
- has a trivial destructor,
- is either
- an aggregate type,
- a type with at least one constexpr (possibly template) constructor that is not a copy or move constructor,
- all non-static data members and base classes are of non-volatile literal types.
Example
literal type that extends string literals:
#include <iostream>
#include <stdexcept>
class conststr
{
const char* p;
std::size_t sz;
public:
template<std::size_t N>
constexpr conststr(const char(&a)[N]) : p(a), sz(N - 1) {}
constexpr char operator[](std::size_t n) const
{
return n < sz? p[n] : throw std::out_of_range("");
}
constexpr std::size_t size() const { return sz; }
};
constexpr std::size_t countlower(conststr s, std::size_t n = 0,
std::size_t c = 0)
{
return n == s.size()? c :
s[n] >= 'a' && s[n] <= 'z'? countlower(s, n + 1, c + 1) :
countlower(s, n + 1, c);
}
// output function that requires a compile-time constant, for testing
template<int n>
struct constN
{
constN() { std::cout << n << '\n'; }
};
int main()
{
std::cout << "the number of lowercase letters in \"Hello, world!\" is ";
constN<countlower("Hello, world!")>(); // implicitly converted to conststr
}Output:
the number of lowercase letters in "Hello, world!" is 9
See also
| (C++11) | checks if a type is literal type (class template) |
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