20 General utilities library [utilities]

20.5 Tuples [tuple]

20.5.3 Class template tuple [tuple.tuple]

20.5.3.2 Assignment [tuple.assign]

For each tuple assignment operator, an exception is thrown only if the assignment of one of the types in Types throws an exception.
In the function descriptions that follow, let i be in the range [0, sizeof...(Types)) in order, be the type in Types, and be the type in a template parameter pack named UTypes, where indexing is zero-based.
constexpr tuple& operator=(const tuple& u);
Effects: Assigns each element of u to the corresponding element of *this.
Returns: *this.
Remarks: This operator is defined as deleted unless is_­copy_­assignable_­v<> is true for all i.
constexpr const tuple& operator=(const tuple& u) const;
Constraints: (is_­copy_­assignable_­v<const Types> && ...) is true.
Effects: Assigns each element of u to the corresponding element of *this.
Returns: *this.
constexpr tuple& operator=(tuple&& u) noexcept(see below);
Constraints: is_­move_­assignable_­v<> is true for all i.
Effects: For all i, assigns std​::​forward<>(get<i>(u)) to get<i>(*this).
Returns: *this.
Remarks: The exception specification is equivalent to the logical AND of the following expressions: is_nothrow_move_assignable_v<> where is the type in Types.
constexpr const tuple& operator=(tuple&& u) const;
Constraints: (is_­assignable_­v<const Types&, Types> && ...) is true.
Effects: For all i, assigns std​::​forward<T>(get<i>(u)) to get<i>(*this).
Returns: *this.
template<class... UTypes> constexpr tuple& operator=(const tuple<UTypes...>& u);
Constraints:
  • sizeof...(Types) equals sizeof...(UTypes) and
  • is_­assignable_­v<&, const &> is true for all i.
Effects: Assigns each element of u to the corresponding element of *this.
Returns: *this.
template<class... UTypes> constexpr const tuple& operator=(const tuple<UTypes...>& u) const;
Constraints:
  • sizeof...(Types) equals sizeof...(UTypes) and
  • (is_­assignable_­v<const Types&, const UTypes&> && ...) is true.
Effects: Assigns each element of u to the corresponding element of *this.
Returns: *this.
template<class... UTypes> constexpr tuple& operator=(tuple<UTypes...>&& u);
Constraints:
  • sizeof...(Types) equals sizeof...(UTypes) and
  • is_­assignable_­v<&, > is true for all i.
Effects: For all i, assigns std​::​forward<>(get<i>(u)) to get<i>(*this).
Returns: *this.
template<class... UTypes> constexpr const tuple& operator=(tuple<UTypes...>&& u) const;
Constraints:
  • sizeof...(Types) equals sizeof...(UTypes) and
  • (is_­assignable_­v<const Types&, UTypes> && ...) is true.
Effects: For all i, assigns std​::​forward<U>(get<i>(u)) to get<i>(*this).
Returns: *this.
template<class U1, class U2> constexpr tuple& operator=(const pair<U1, U2>& u);
Constraints:
  • sizeof...(Types) is 2 and
  • is_­assignable_­v<&, const U1&> is true, and
  • is_­assignable_­v<&, const U2&> is true.
Effects: Assigns u.first to the first element of *this and u.second to the second element of *this.
Returns: *this.
template<class U1, class U2> constexpr const tuple& operator=(const pair<U1, U2>& u) const;
Constraints:
  • sizeof...(Types) is 2,
  • is_­assignable_­v<const &, const U1&> is true, and
  • is_­assignable_­v<const &, const U2&> is true.
Effects: Assigns u.first to the first element and u.second to the second element.
Returns: *this.
template<class U1, class U2> constexpr tuple& operator=(pair<U1, U2>&& u);
Constraints:
  • sizeof...(Types) is 2 and
  • is_­assignable_­v<&, U1> is true, and
  • is_­assignable_­v<&, U2> is true.
Effects: Assigns std​::​forward<U1>(u.first) to the first element of *this and
std​::​forward<U2>(u.second) to the second element of *this.
Returns: *this.
template<class U1, class U2> constexpr const tuple& operator=(pair<U1, U2>&& u) const;
Constraints:
  • sizeof...(Types) is 2,
  • is_­assignable_­v<const &, U1> is true, and
  • is_­assignable_­v<const &, U2> is true.
Effects: Assigns std​::​forward<U1>(u.first) to the first element and
std​::​forward<U2>(u.second) to the second element.
Returns: *this.