C++ concepts: LiteralType
From cppreference.com
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.
[edit] Requirements
A literal type is any of the following
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(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:
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- has a trivial destructor,
- is either
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- 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.
[edit] Example
literal type that extends string literals:
Run this code
#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 << "Number of lowercase letters in \"Hello, world!\" is "; constN<countlower("Hello, world!")>(); // implicitly converted to conststr }
Output:
Number of lowercase letters in "Hello, world!" is 9
[edit] See also
(C++11)
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checks if a type is literal type (class template) |