compile time bounds checking proof of concept

static_bounds_checking.cpp

template<long MIN, long MAX>
struct BoundedInteger
{
    BoundedInteger()
    {
        value_ = MIN;
    }

    BoundedInteger(long value)
    {
        if (value < MIN) value = MIN;
        if (value > MAX) value = MAX;

        value_ = value;
    }

    operator long&() { return value_; }

    long value_{};
    static constexpr long MIN_VAL = MIN;
    static constexpr long MAX_VAL = MAX;
};

template<long I>
using ConstantInteger = BoundedInteger<I,I>;


template<long MIN_L, long MAX_L, long MIN_R, long MAX_R>
auto operator+(
    BoundedInteger<MIN_L, MAX_L> left, 
    BoundedInteger<MIN_R, MAX_R> right)
-> BoundedInteger<MIN_L + MIN_R, MAX_R + MAX_L>
{
    return left.value_ + right.value_;
}

#include <iostream>
int main()
{
    BoundedInteger<30, 45> ival{};
    std::cin >> ival;

    auto result = ConstantInteger<5>{} + ival;
    static_assert(result.MAX_VAL <= 50);
    static_assert(result.MIN_VAL >= 35);

    std::cout << result;
}