Question

I need a bitset with a slightly diffrent behavior when asigning variables with integer type to a specific bit. The bit should be set to zero if the assigned integer is smaller then one, and to one elsewise.

As a simple solution I copied the STL bitset, replaced the classname with altbitset, adjusted namespaces and include guard and added following function under reference& operator=(bool __x) in the nested reference class:

template <typename T> 
reference& operator=(T i) {
    if (i<1) return operator=(false);
    return operator=(true);
}

It works as expected.

Question is if there is a better way doing this.

Answer 1

You shouldn’t copy a library just to add a new function. Not only that, the new function is wildly unintuitive and could possibly be the source of errors for even just reading the code, let alone writing it.

Before:

bv[n] = -1; // I know a Boolean conversion on -1 will take place
assert(bv[n]); // of course, since -1 as a Boolean is true

After:

bv[n] = -1; // I guess an integer < 1 means false?
assert(bv[n]); // Who changed my bitvector semantics?!

Just write it out so it makes sense in your domain:

bv[n] = (i < 1);

Remember: simplest doesn’t always mean fewest characters, it means clearest to read.

---

If you do want to extend the functionality of existing types, you should do so with free functions:

template <typename BitSet, typename Integer>
auto assign_bit_integer(BitSet& bits, const std::size_t bit, const Integer integer) ->
    typename std::enable_if<std::is_integral<Integer>::value,
                            typename BitSet::reference>::type
{
    return bits[bit] = (integer < 1);
}

Giving:

std::bitset<8> bits;

assign_bit_integer(bits, 0, 5);
// ERROR: assign_bit_integer(bits, 0, 5.5);

But for such a small function with no clear “obvious” name that describes what it does concisely(assign_bit_true_if_less_than_one_otherwise_false is verbose, to say the least), just write out the code; it says the same thing anyway.