template< class... Types >
class tuple;
Class template std::tuple is a fixed-size collection of heterogeneous values. It is a generalization of std::pair.
If std::is_trivially_destructible<Ti>::value is true for every Ti in Types, the destructor of std::tuple is trivial.
If a program declares an explicit or partial specialization of std::tuple, the program is ill-formed, no diagnostic required.
tuple
tuple to another
tuples
constexpr bool enable_nonlocking_formatter_optimization<std::tuple<Ts...>>
This specialization of std::enable_nonlocking_formatter_optimization enables efficient implementation of std::print and std::println for printing a tuple object when each element type enables it.
Since the "shape" of a tuple â its size, the types of its elements, and the ordering of those types â are part of its type signature, they must all be available at compile time and can only depend on other compile-time information. This means that many conditional operations on tuples â in particular, conditional prepend/append and filter â are only possible if the conditions can be evaluated at compile time. For example, given a std::tuple<int, double, int>, it is possible to filter on types â e.g. returning a std::tuple<int, int> â but not to filter on whether or not each element is positive (which would have a different type signature depending on runtime values of the tuple), unless all the elements were themselves constexpr.
As a workaround, one can work with tuples of std::optional, but there is still no way to adjust the size based on runtime information.
Until N4387 (applied as a defect report for C++11), a function could not return a tuple using copy-list-initialization:
std::tuple<int, int> foo_tuple()
{
return {1, -1}; // Error until N4387
return std::tuple<int, int>{1, -1}; // Always works
return std::make_tuple(1, -1); // Always works
}[edit] Example
#include <iostream>
#include <stdexcept>
#include <string>
#include <tuple>
std::tuple<double, char, std::string> get_student(int id)
{
switch (id)
{
case 0: return {3.8, 'A', "Lisa Simpson"};
case 1: return {2.9, 'C', "Milhouse Van Houten"};
case 2: return {1.7, 'D', "Ralph Wiggum"};
case 3: return {0.6, 'F', "Bart Simpson"};
}
throw std::invalid_argument("id");
}
int main()
{
const auto student0 = get_student(0);
std::cout << "ID: 0, "
<< "GPA: " << std::get<0>(student0) << ", "
<< "grade: " << std::get<1>(student0) << ", "
<< "name: " << std::get<2>(student0) << '\n';
const auto student1 = get_student(1);
std::cout << "ID: 1, "
<< "GPA: " << std::get<double>(student1) << ", "
<< "grade: " << std::get<char>(student1) << ", "
<< "name: " << std::get<std::string>(student1) << '\n';
double gpa2;
char grade2;
std::string name2;
std::tie(gpa2, grade2, name2) = get_student(2);
std::cout << "ID: 2, "
<< "GPA: " << gpa2 << ", "
<< "grade: " << grade2 << ", "
<< "name: " << name2 << '\n';
// C++17 structured binding:
const auto [gpa3, grade3, name3] = get_student(3);
std::cout << "ID: 3, "
<< "GPA: " << gpa3 << ", "
<< "grade: " << grade3 << ", "
<< "name: " << name3 << '\n';
}
Output:
ID: 0, GPA: 3.8, grade: A, name: Lisa Simpson ID: 1, GPA: 2.9, grade: C, name: Milhouse Van Houten ID: 2, GPA: 1.7, grade: D, name: Ralph Wiggum ID: 3, GPA: 0.6, grade: F, name: Bart Simpson[edit] 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 2796 C++11 triviality of the destructor ofstd::tuple was unspecified specified LWG 3990 C++11 a program could declare an explicit or
std::tuple the program is ill-formed in this
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