Methods directly on containers (e.g `maybe`)

[tom91136]

I was wondering would adding a few more methods to some of the containers would help with productivity. For example:

    auto o = fplus::maybe<int>(1);
    auto p = fwd::apply(
        o,
        fwd::and_then_maybe([](auto x) { return x > 0 ? fplus::just(1) : fplus::nothing<int>(); }),
        fwd::lift_maybe([](auto x) { return x * 2; }),
        fwd::just_with_default(42)
    );

    auto p2 = o
            .and_then([](auto x) { return x > 0 ? fplus::just(1) : fplus::nothing<int>(); })
            .lift([](auto x) { return x * 2; })
            .get_with_default(42);

That way:

• It aligns with the C++23 monadic interfaces on optional
• We can drop the _maybe suffix as it's clear based on the method receiver
• We should still keep the free functions but those simply delegates to the instance implementation, so we don't need to forward declare it or do anything awkward.
• For most cases (e.g chaining on the same functor), we can get the same effect of using fwd but without the extra boilerplate.

I'm happy to open a PR if we think this is a good idea.

[Dobiasd]

Oh, that looks like a splendid idea to me in terms of code readability. :heart:

Yeah, we should keep the free functions (to not break old client code). And, I agree, letting the free functions forward to the member functions (instead of the other way around) is the way to go, exactly because of the reason you mentioned. :+1:

I'd be happy to receive your PR. :slightly_smiling_face: