unordered_set operator= in C++ STL

The '=' is an operator in C++ STL which copies (or moves) an unordered_set to another unordered_set and unordered_set::operator= is the corresponding operator function. There are three versions of this function.

• The first version takes reference of an unordered_set as an argument and copies it to an unordered_set.
• The second version performs a move assignment i.e it moves the content of an unordered_set to another unordered_set.
• The third version assigns contents of an initializer list to an unordered_set.

Syntax

uset.operator= ( unordered_set& us )
uset.operator= ( unordered_set&& us )
uset.operator= ( initializer list )

Parameters:

• The first version takes the reference of an unordered_set as argument.
• The second version takes the r-value reference of an unordered_set as argument.
• The third version takes an initializer list as argument.

Return value: All of them returns the value of this pointer(*this) . Below program illustrates the unordered_set::operator= in C++. 

Program: 

// C++ code to illustrate the method 
// unordered_set::operator=() 
#include <iostream> 
#include <unordered_set> 
using namespace std; 

// merge function 
template <class T> 
T merge(T a, T b) 
{ 
    T t(a); 
    t.insert(b.begin(), b.end()); 
    return t; 
} 

int main() 
{ 
    unordered_set<int> sample1, sample2, sample3; 
    
    // List initialization 
    sample1 = { 7, 8, 9 }; 
    sample2 = { 9, 10, 11, 12 }; 
    
    // Merge both lists 
    sample3 = merge(sample1, sample2); 
    
    // copy assignment 
    sample1 = sample3; 

    // Print the unordered_set list 
    for (auto it = sample1.begin(); it != sample1.end(); ++it) 
        cout << *it << " "; 
    cout << endl; 

    for (auto it = sample2.begin(); it != sample2.end(); ++it) 
        cout << *it << " "; 
    cout << endl; 

    for (auto it = sample3.begin(); it != sample3.end(); ++it) 
        cout << *it << " "; 
    cout << endl; 
} 

10 11 12 7 8 9 
12 11 10 9 
10 11 12 7 8 9

Time complexity: O(n)
Auxiliary Space: O(n)