[C++] Wskaźnik this i constant

#include <iostream>
#include <vector>
#include <algorithm>


class IsEqual {
    int value;
public:
    IsEqual( int v )
        : value( v )
    { }
    bool operator ()( const int & elem ) {
        this->value = 6;
        return elem == value;
    }
};

int main()
{
    const IsEqual tst( 2 );
    std::vector < int > vec = { 3, 2, 1, 4, 3, 7, 8, 6 };
    std::replace_if( vec.begin(), vec.end(), tst, 5 );
    for( int i: vec ) std::cout << i << " ";
   
    std::cout << std::endl;
}