Question

I don’t know if it’s possible but I want to do stuff like

int someval = 1;
if({1,2,3,4}_v.contains(someval ))

but when I try to define literal as:

std::vector<int> operator"" _v ( std::initializer_list<int> t )
{
    return std::vector<int> (t);
}

to accept initializer list of ints I get

 error: 'std::vector<int> operator"" _v(std::initializer_list<int> t)' has invalid argument list

Is there a way to do this? What I really want is to finally be rid of stuff like

if(value == 1 || value ==2 || value == 3 ...

Having to write stuff like this is really annoying, because you’d expect syntax to be

if value in (value1, value2 ...) 

or something similar.

Answer 1

you’d expect syntax to be

if value in (value1, value2 ...) 

or something similar.

If you’re willing to add one extra character, try this syntax:

#include <algorithm>
#include <iostream>
#include <array>

template <typename T0, typename T1, std::size_t N>
bool operator *(const T0& lhs, const std::array<T1, N>& rhs) {
  return std::find(begin(rhs), end(rhs), lhs) != end(rhs);
}

template<class T0, class...T> std::array<T0, 1+sizeof...(T)> in(T0 arg0, T...args) {
  return {{arg0, args...}};
}

int main () {
  if( 2 *in(1,2,3) ) { std::cout << "Hello\n"; }
  if( 4 *in(5,6,7,8) ) { std::cout << "Goodbye\n"; }
}