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# std::valarray::operator=

From cppreference.com
< cpp‎ | numeric‎ | valarray

valarray<T>& operator=( const valarray<T>& other ); | (1) |
valarray<T>& operator=( valarray<T>&& other ); | (2) | (since C++11)
valarray<T>& operator=( const T& val ); | (3) |
valarray<T>& operator=( const std::slice_array& other); | (4) |
valarray<T>& operator=( const std::gslice_array& other); | (5) |
valarray<T>& operator=( const std::mask_array& other ); | (6) |
valarray<T>& operator=( const std::indirect_array& other ); | (7) |
valarray<T>& operator=( std::initializer_list<T> il ); | (8) | (since C++11)

Replaces the contents of the numeric array.

1) Copy assignment operator. If the length of `other` does not equal the length of `*this`, first resizes as if by resize(other.size()), then replaces each element of `*this` with a copy of the corresponding element of `other`
2) Move assignment operator. Replaces the contents of `*this` with those of `other`. The value of `other` is unspecified after this operation. The complexity of this operation may be linear if T has non-trivial destructors, but is usually constant otherwise.
3) Replaces each value in `*this` with a copy of `val`.
4-7) Replaces the contents of `*this` with the result of a generalized subscripting operation. The behavior is undefined if the length of the argument does not equal the length of `*this` or if any value on the left depends on the value on the right (e.g v=v[v>2]).
8) Assigns the contents of initializer list `il`. Equivalent to *this = valarray(il).

### [edit] Parameters

other | - | another numeric array (or a mask) to assign
val | - | the value to initialize each element with
il | - | initializer list to assign

### [edit] Return value

*this

### [edit] Exceptions

1) (none)
2)
`noexcept` specification:
noexcept
3-8) (none)

### [edit] Example

Run this code

    #include <valarray>
    #include <iostream>

    int main()
    {
        std::valarray<int> v1(3);
        v1 = -1; // from a scalar
        std::cout << "assigned from scalar: ";
        for(int n: v1) std::cout << n << ' '; std::cout << '\n';

        v1 = {1, 2, 3, 4, 5, 6}; // from initializer list of different size
        std::cout << "assigned from initializer_list:      ";
        for(int n: v1) std::cout << n << ' '; std::cout << '\n';

        std::valarray<int> v2(3);
        v2 = v1[std::slice(0,3,2)]; // from slice array
        std::cout << "every 2nd element starting at pos 0: ";
        for(int n: v2) std::cout << n << ' '; std::cout << '\n';

        v2 = v1[v1 % 2 == 0]; // from mask array
        std::cout << "values that are even          :      ";
        for(int n: v2) std::cout << n << ' '; std::cout << '\n';

        std::valarray<std::size_t> idx = {0,1,2,4}; // index array
        v2.resize(4); // sizes must match when assigning from gen subscript
        v2 = v1[idx]; // from indirect array
        std::cout << "values at positions 0,1,2,4:         ";
        for(int n: v2) std::cout << n << ' '; std::cout << '\n';
    }

Output:

    assigned from scalar: -1 -1 -1
    assigned from initializer_list:      1 2 3 4 5 6
    every 2nd element starting at pos 0: 1 3 5
    values that are even          :      2 4 6
    values at positions 0,1,2,4:         1 2 3 5

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- unconditionally noexcept