# std::tuple

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Defined in header `<tuple>` |  |
template< class... Types > class tuple; |  | (since C++11)

Class template `std::tuple` is a fixed-size collection of heterogeneous values. It is a generalization of std::pair.

If (std::is_trivially_destructible_v<Types> && ...) is true, the destructor of `tuple` is trivial. | (since C++17)

### Template parameters

Types... | - | the types of the elements that the tuple stores. Empty list is supported.

### Member functions

(constructor) | constructs a new `tuple` (public member function)
operator= | assigns the contents of one `tuple` to another (public member function)
swap | swaps the contents of two `tuple`s (public member function)

### Non-member functions

make_tuple | creates a `tuple` object of the type defined by the argument types (function template)
tie | creates a `tuple` of lvalue references or unpacks a tuple into individual objects (function template)
forward_as_tuple | creates a `tuple` of rvalue references (function template)
tuple_cat | creates a `tuple` by concatenating any number of tuples (function template)
std::get(std::tuple) | tuple accesses specified element (function template)
operator==operator!=operator<operator<=operator>operator>= | lexicographically compares the values in the tuple (function template)
std::swap(std::tuple) (C++11) | specializes the std::swap algorithm (function template)

### Helper classes

tuple_size | obtains the size of `tuple` at compile time (class template specialization)
tuple_element | obtains the type of the specified element (class template specialization)
std::uses_allocator<std::tuple> (C++11) | specializes the std::uses_allocator type trait (class template specialization)
ignore | placeholder to skip an element when unpacking a `tuple` using `tie` (constant)

### Deduction guides(since C++17)

### Notes

Until C++17, a function could not return a tuple using list-initialization:

    std::tuple<int, int> foo_tuple()
    {
      return {1, -1};  // Error until C++17
      return std::make_tuple(1, -1); // Always works
    }

### Example

Run this code

    #include <tuple>
    #include <iostream>
    #include <string>
    #include <stdexcept>

    std::tuple<double, char, std::string> get_student(int id)
    {
        if (id == 0) return std::make_tuple(3.8, 'A', "Lisa Simpson");
        if (id == 1) return std::make_tuple(2.9, 'C', "Milhouse Van Houten");
        if (id == 2) return std::make_tuple(1.7, 'D', "Ralph Wiggum");
        throw std::invalid_argument("id");
    }

    int main()
    {
        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';

        double gpa1;
        char grade1;
        std::string name1;
        std::tie(gpa1, grade1, name1) = get_student(1);
        std::cout << "ID: 1, "
                  << "GPA: " << gpa1 << ", "
                  << "grade: " << grade1 << ", "
                  << "name: " << name1 << '\n';

        // C++17 structured binding:
        auto [ gpa2, grade2, name2 ] = get_student(2);
        std::cout << "ID: 2, "
                  << "GPA: " << gpa2 << ", "
                  << "grade: " << grade2 << ", "
                  << "name: " << name2 << '\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

### References

- C++11 standard (ISO/IEC 14882:2011):

  - 20.4 Tuples [tuple]

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