Comparison tricks in C++

Question

A class:

class foo{
public:
    int data;
};

Now I want to add a method to this class, to do some comparison, to see if its data is equal to on

Answer 1

set is a good option, but if you really want to roll your own, initializer_list is convienient:

bool is_in( int val, initializer_list lst )
{
    for( auto i : lst )
        if( i == val ) return true;
    return false;
}

use is trivial:

is_in( x, { 3, 5, 7 } ) ;

it's O(n) thou, set / unordered is faster