Example Either type in C++

either.cpp

#include <stdio.h>

template <class T1, class T2> 
class Either
{
    bool isLeft;
    union
    {
        T1 left;
        T2 right;    
    };
    template<class T1_, class T2_> friend Either<T1_, T2_> Left(T1_ x);
    template<class T1_, class T2_> friend Either<T1_, T2_> Right(T1_ x);
public:
    bool matchLeft(T1& x)
    {
        if (isLeft)
            x = left;
        return isLeft;    
    }
    bool matchRight(T2& x)
    {
        if (!isLeft)
            x = right;
        return !isLeft;    
    }  
};

template <class T1, class T2> 
Either<T1, T2> Left(T1 x)
{
    Either<T1, T2> e;
    e.isLeft = true;
    e.left = x;
    return e;
}
template <class T1, class T2> 
Either<T1, T2> Right(T2 x)
{
    Either<T1, T2> e;
    e.isLeft = false;
    e.right = x;
    return e;
}

int main(int argc, char* argv[])
{
  Either<int, float> x = Left<int, float>(5);
  int c;
  if (x.matchLeft(c))
    printf("the number is %i", c);
  return 0;
}

I'm using Arduino like chip with c++11 but no std lib or exceptions support. I end up defining sth like that:

#pragma once

template <class L, class R> 
class Either
{
    virtual bool isLeft();
    virtual bool isRight();

    virtual bool matchLeft(L& x);
    virtual bool matchRight(R& x);
};

template <class L, class R> 
class Left : public Either<L, R> {
public:
    L left;

    Left(L left): left(left) {}
    constexpr bool isLeft() { return true; }
    constexpr bool isRight() { return false; }

    bool matchLeft(L& x)
    {
        x = left;
        return true;
    }
    bool matchRight(R& x) { return false; }
};

template <class L, class R> 
class Right : public Either<L, R> {
public:
    R right;

    Right(R right): right(right) {}
    constexpr bool isLeft() { return false; }
    constexpr bool isRight() { return true; }

    bool matchLeft(L& x) { return false; }

    bool matchRight(R& x) {
        x = right;
        return true;
    }
};

I'm not native C++ dev so I would be glad for comments.

Are you sure you meant
template<class T1_, class T2_> friend Either<T1_, T2_> Right(T1_ x);
not
template<class T1_, class T2_> friend Either<T1_, T2_> Right(T2_ x);
?