std::tuple<Types...>::operator= - cppreference.com (original) (raw)

tuple& operator=( const tuple& other );	(1)	(since C++11) (constexpr since C++20)
constexpr const tuple& operator=( const tuple& other ) const;	(2)	(since C++23)
tuple& operator=( tuple&& other ) noexcept(/* see below */);	(3)	(since C++11) (constexpr since C++20)
constexpr const tuple& operator=( tuple&& other ) const;	(4)	(since C++23)
template< class... UTypes >tuple& operator=( const tuple<UTypes...>& other );	(5)	(since C++11) (constexpr since C++20)
template< class... UTypes > constexpr const tuple& operator=( const tuple<UTypes...>& other ) const;	(6)	(since C++23)
template< class... UTypes >tuple& operator=( tuple<UTypes...>&& other );	(7)	(since C++11) (constexpr since C++20)
template< class... UTypes > constexpr const tuple& operator=( tuple<UTypes...>&& other ) const;	(8)	(since C++23)
template< class E1, class E2 >tuple& operator=( const std::pair<E1, E2>& p );	(9)	(since C++11) (constexpr since C++20)
template< class E1, class E2 > constexpr const tuple& operator=( const std::pair<E1, E2>& p ) const;	(10)	(since C++23)
template< class E1, class E2 >tuple& operator=( std::pair<E1, E2>&& p );	(11)	(since C++11) (constexpr since C++20)
template< class E1, class E2 > constexpr const tuple& operator=( std::pair<E1, E2>&& p ) const;	(12)	(since C++23)
template< tuple-like UTuple > constexpr tuple& operator=( UTuple&& u );	(13)	(since C++23)
template< tuple-like UTuple > constexpr const tuple& operator=( UTuple&& u ) const;	(14)	(since C++23)

Replaces the contents of the tuple with the contents of another tuple-like object.

In the descriptions that follow, let

i be in the range [0, sizeof...(Types)) in order,
Ti be the ith type in the class template parameter pack Types, and
Ui be the ith type in a function template parameter pack named UTypes,

where indexing is zero-based.

Copy assignment operator. Assigns each element of other to the corresponding element of *this.

This overload is defined as deleted unless std::is_copy_assignable<Ti>::value is true for all Ti.

Copy assignment operator for const-qualified operand. Assigns each element of other to the corresponding element of *this.

This overload participates in overload resolution only if std::is_copy_assignable_v<const Ti> is true for all Ti.

Move assignment operator. For all i, assigns std::forward<Ti>(std::get(other)) to std::get(*this).

This overload participates in overload resolution only if std::is_move_assignable<Ti>::value is true for all Ti.

Move assignment operator for const-qualified operand. For all i, assigns std::forward<Ti>(std::get(other)) to std::get(*this).

This overload participates in overload resolution only if std::is_assignable_v<const Ti&, Ti> is true for all Ti.

For all i, assigns std::get(other) to std::get(*this).

This overload participates in overload resolution only if sizeof...(Types) == sizeof...(UTypes), and std::is_assignable<Ti&, const Ui&>::value is true for all corresponding pairs of types Ti and Ui.

For all i, assigns std::get(other) to std::get(*this).

This overload participates in overload resolution only if sizeof...(Types) == sizeof...(UTypes), and std::is_assignable_v<const Ti&, const Ui&> is true for all corresponding pairs of types Ti and Ui.

For all i, assigns std::forward<Ui>(std::get(other)) to std::get(*this).

This overload participates in overload resolution only if sizeof...(Types) == sizeof...(UTypes), and std::is_assignable<Ti&, Ui>::value is true for all corresponding pairs of types Tiand Ui.

For all i, assigns std::forward<Ui>(std::get(other)) to std::get(*this).

This overload participates in overload resolution only if sizeof...(Types) == sizeof...(UTypes), and std::is_assignable_v<const Ti&, Ui> is true for all corresponding pairs of types Ti and Ui.

Assigns p.first to the first element of *this and p.second to the second element of *this.

This overload participates in overload resolution only if

sizeof...(Types) == 2,
std::is_assignable<T0&, const E1&>::value is true, and
std::is_assignable<T1&, const E2&>::value is true.

Assigns p.first to the first element and p.second to the second element.
Assigns std::forward<E1>(p.first) to the first element of *this and std::forward<E2>(p.second) to the second element of *this.
Assigns std::forward<E1>(p.first) to the first element and std::forward<E2>(p.second) to the second element.
For all i, assigns std::get(std::forward<UTuple>(u)) to std::get(*this).
For all i, assigns std::get(std::forward<UTuple>(u)) to std::get(*this).

[edit] Parameters

other	-	tuple to replace the contents of this tuple
p	-	pair to replace the contents of this 2-tuple
u	-	tuple-like object to replace the contents of this tuple

[edit] Return value

*this

[edit] Exceptions

1,2) May throw implementation-defined exceptionsif the assignment of one of the types in Types throws an exception.

4-14) May throw implementation-defined exceptionsif the assignment of one of the types in Types throws an exception.

[edit] Example

#include #include #include #include #include #include // helper function to print std::vector std::ostream& operator<<(std::ostream& os, std::vector const& v) { os << '{'; for (std::size_t t = 0; t != v.size(); ++t) os << v[t] << (t + 1 < v.size() ? ", " : ""); return os << '}'; } // helpers to print a tuple of any size template<class... Args> void print_tuple(std::string_view name, const std::tuple<Args...>& t) { std::cout << name << " = {"; std::apply([&](auto&& arg, auto&&... args) { std::cout << arg; ((std::cout << ", " << args), ...); }, t); std::cout << '}'; } template<class Tuple1, class Tuple2> void print_tuples(std::string_view name1, const Tuple1& t1, std::string_view name2, const Tuple2& t2) { print_tuple(name1, t1); std::cout << ", "; print_tuple(name2, std::tuple(t2)); std::cout << "\n\n"; } int main() { // Tuple to tuple examples // std::tuple<int, std::string, std::vector> t1{1, "alpha", {1, 2, 3}}, t2{2, "beta", {4, 5}}; print_tuples("1) t1", t1, "t2", t2); // Normal copy assignment // operator=( const tuple& other ); t1 = t2; print_tuples("2) t1 = t2;\n t1", t1, "t2", t2); // Normal move assignment // operator=( tuple&& other ); t1 = std::move(t2); print_tuples("3) t1 = std::move(t2);\n t1", t1, "t2", t2); // Converting copy assignment // operator=( const tuple<UTypes...>& other ); std::tuple<short, const char*, std::vector> t3{3, "gamma", {6, 7, 8}}; t1 = t3; print_tuples("4) t1 = t3;\n t1", t1, "t3", t3); // Converting move assignment // operator=( tuple<UTypes...>&& other ); t1 = std::move(t3); print_tuples("5) t1 = std::move(t3);\n t1", t1, "t3", t3); // Pair to tuple examples // std::tuple<std::string, std::vector> t4{"delta", {10, 11, 12}}; std::pair<const char*, std::vector> p1{"epsilon", {14, 15, 16}}; print_tuples("6) t4", t4, "p1", p1); // Converting copy assignment from std::pair // operator=( const std::pair<U1, U2>& p ); t4 = p1; print_tuples("7) t4 = p1;\n t4", t4, "p1", p1); // Converting move assignment from std::pair // operator=( std::pair<U1, U2>&& p ); t4 = std::move(p1); print_tuples("8) t4 = std::move(p1);\n t4", t4, "p1", p1); }

Possible output:

t1 = {1, alpha, {1, 2, 3}}, t2 = {2, beta, {4, 5}}
t1 = t2; t1 = {2, beta, {4, 5}}, t2 = {2, beta, {4, 5}}
t1 = std::move(t2); t1 = {2, beta, {4, 5}}, t2 = {2, , {}}
t1 = t3; t1 = {3, gamma, {6, 7, 8}}, t3 = {3, gamma, {6, 7, 8}}
t1 = std::move(t3); t1 = {3, gamma, {6, 7, 8}}, t3 = {3, gamma, {}}
t4 = {delta, {10, 11, 12}}, p1 = {epsilon, {14, 15, 16}}
t4 = p1; t4 = {epsilon, {14, 15, 16}}, p1 = {epsilon, {14, 15, 16}}
t4 = std::move(p1); t4 = {epsilon, {14, 15, 16}}, p1 = {epsilon, {}}

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.