Class expression

test/include/test.hpp:241–877

template <class T, class U, class Operator>
struct expression
{
    T lhs;
    U rhs;

    friend std::ostream& operator<<(std::ostream& s, const expression& self)
    {
        print_stream(s, self.lhs);
        s << " " << Operator::as_string() << " ";
        print_stream(s, self.rhs);
        return s;
    }

    friend decltype(auto) get_value(const expression& e) { return e.value(); }

    decltype(auto) value() const { return Operator::call(get_value(lhs), get_value(rhs)); };

    TEST_FOREACH_UNARY_OPERATORS(TEST_EXPR_UNARY_OPERATOR)
    TEST_FOREACH_BINARY_OPERATORS(TEST_EXPR_BINARY_OPERATOR)
};

// TODO: Remove rvalue references
template <class T, class U, class Operator>
expression<T, U, Operator> make_expression(T&& lhs, U&& rhs, Operator)
{
    return {std::forward<T>(lhs), std::forward<U>(rhs)};
}

// TODO: Remove rvalue reference
template <class T>
lhs_expression<T> make_lhs_expression(T&& lhs)
{
    return lhs_expression<T>{std::forward<T>(lhs)};
}

template <class T, class Operator>
lhs_expression<T, Operator> make_lhs_expression(T&& lhs, Operator)
{
    return lhs_expression<T, Operator>{std::forward<T>(lhs)};
}

template <class T, class Operator>
struct lhs_expression
{
    T lhs;
    explicit lhs_expression(T e) : lhs(std::move(e)) {}

    friend std::ostream& operator<<(std::ostream& s, const lhs_expression& self)
    {
        std::string op = Operator::as_string();
        if(not op.empty())
            s << Operator::as_string() << " ";
        print_stream(s, self.lhs);
        return s;
    }

    friend decltype(auto) get_value(const lhs_expression& e) { return e.value(); }