std::tuple(3)

NAME
std::tuple - std::tuple

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

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 tuples
                 (public member function)

Non-member functions
   make_tuple creates a tuple object of the type defined by the argument
   (C++11) types
                        (function template)
   tie creates a tuple of lvalue references or unpacks a tuple into
   (C++11) individual objects
                        (function template)
   forward_as_tuple creates a tuple of forwarding references
   (C++11) (function template)
   tuple_cat creates a tuple by concatenating any number of tuples
   (C++11) (function template)
   get(std::tuple) tuple accesses specified element
   (C++11) (function template)
   operator==
   operator!=
   operator<
   operator<=
   operator>
   operator>= lexicographically compares the values in the tuple
   operator<=> (function template)
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (C++20)
   std::swap(std::tuple) specializes the std::swap algorithm
   (C++11) (function template)
   Helper concepts
   tuple-like specifies that a type implemented the tuple protocol
   pair-like (std::get, std::tuple_element, std::tuple_size)
   (C++23) (exposition-only concept*)

Helper classes
   std::tuple_size<std::tuple> obtains the size of tuple at compile time
   (C++11) (class template specialization)
   std::tuple_element<std::tuple> obtains the type of the specified element
   (C++11) (class template specialization)
   std::uses_allocator<std::tuple> specializes the std::uses_allocator type
   (C++11) trait
                        (class template specialization)
   std::basic_common_reference<tuple-like> determines the common reference type of a
   (C++23) tuple and a tuple-like type
                        (class template specialization)
   std::common_type<tuple-like> determines the common type of a tuple and a
   (C++23) tuple-like type
                        (class template specialization)
   std::formatter<std::tuple> formatting support for tuple
   (C++23) (class template specialization)
   ignore placeholder to skip an element when
   (C++11) unpacking a tuple using tie
                        (constant)
   Deduction guides (since C++17)

Notes
   Since the "shape" of a tuple – its size, the types of its elements, and the ordering
   of those types – 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 – in particular, conditional prepend/append
   and filter – 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
   – e.g. returning a std::tuple<int, int> – 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
 }

Example
// Run this code
 #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
   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 of specified
                       std::tuple was unspecified
                        the program is ill-formed
   LWG 3990 C++11 a program could declare an explicit or in this
                       partial specialization of std::tuple case (no diagnostic
                        required)

References
     * C++23 standard (ISO/IEC 14882:2023):
     * 22.4 Tuples [tuple]
     * C++20 standard (ISO/IEC 14882:2020):
     * 20.5 Tuples [tuple]
     * C++17 standard (ISO/IEC 14882:2017):
     * 23.5 Tuples [tuple]
     * C++14 standard (ISO/IEC 14882:2014):
     * 20.4 Tuples [tuple]
     * C++11 standard (ISO/IEC 14882:2011):
     * 20.4 Tuples [tuple]

See also
   pair implements binary tuple, i.e. a pair of values
        (class template)