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std optional is based on boost optional which was written in 2003 before any sort of lambdas made monadic operations usable. The main concern with that compone

std optional is based on boost optional which was written in 2003 before any sort of lambdas made monadic operations usable. The main concern with that component was ensuring we can allocate stack storage for an object that may or may not be initialized. The reference is easily achievable by using T* so is of minimal value, but also poses some more semantic problems since a reference is not copyable while an optional is.

tialaramex 2y ago
I actually don't care that much about the monadic functions. For me the important use case is pattern matching, which C++ doesn't yet have. Pattern matching really changes how you see the entire language.
- mgaunard 2y ago
  C++ has pattern matching through overloading.
  - tialaramex 2y ago
    How do you figure?
    - mgaunard 2y ago
      I don't understand the question. Here is the first example I found on Google if that helps you understand. std::variant<Fluid, LightItem, HeavyItem, FragileItem> package; std::visit(overload{ [](Fluid& ) { std::cout << "fluid\n"; }, [](LightItem& ) { std::cout << "light item\n"; }, [](HeavyItem& ) { std::cout << "heavy item\n"; }, [](FragileItem& ) { std::cout << "fragile\n"; } }, package);
      - tialaramex 2y ago
        But that's not really even a pattern match? Here's what a pattern match looks like: [This is from day 10 of last year's Advent of Code.] match (state, pipe) { (State::None, Pipe::Ground) => { if inside { n += 1; } } (State::None, Pipe::Vert) => { inside = !inside; } (State::None, Pipe::Se) => { state = State::South; } (State::None, Pipe::Ne) => { state = State::North; } // Horizontal lines make no difference to anything (State::North | State::South, Pipe::Horiz) => {} // U-turns (State::South, Pipe::Sw) | (State::North, Pipe::Nw) => { state = State::None; } // Form a vertical line (State::South, Pipe::Nw) | (State::North, Pipe::Sw) => { inside = !inside; state = State::None; } _ => { panic!("Unexpected sequence {state:?} {pipe:?}"); } }
        mgaunard 2y ago
        This is the exact same thing except you're visiting two arguments at a time. Guess what, the same syntax I gave supports exactly that as well.

tialaramex 2y ago

I actually don't care that much about the monadic functions. For me the important use case is pattern matching, which C++ doesn't yet have. Pattern matching really changes how you see the entire language.

mgaunard 2y ago
C++ has pattern matching through overloading.
- tialaramex 2y ago
  How do you figure?
  - mgaunard 2y ago
    I don't understand the question. Here is the first example I found on Google if that helps you understand. std::variant<Fluid, LightItem, HeavyItem, FragileItem> package; std::visit(overload{ [](Fluid& ) { std::cout << "fluid\n"; }, [](LightItem& ) { std::cout << "light item\n"; }, [](HeavyItem& ) { std::cout << "heavy item\n"; }, [](FragileItem& ) { std::cout << "fragile\n"; } }, package);
    - tialaramex 2y ago
      But that's not really even a pattern match? Here's what a pattern match looks like: [This is from day 10 of last year's Advent of Code.] match (state, pipe) { (State::None, Pipe::Ground) => { if inside { n += 1; } } (State::None, Pipe::Vert) => { inside = !inside; } (State::None, Pipe::Se) => { state = State::South; } (State::None, Pipe::Ne) => { state = State::North; } // Horizontal lines make no difference to anything (State::North | State::South, Pipe::Horiz) => {} // U-turns (State::South, Pipe::Sw) | (State::North, Pipe::Nw) => { state = State::None; } // Form a vertical line (State::South, Pipe::Nw) | (State::North, Pipe::Sw) => { inside = !inside; state = State::None; } _ => { panic!("Unexpected sequence {state:?} {pipe:?}"); } }
      - mgaunard 2y ago
        This is the exact same thing except you're visiting two arguments at a time. Guess what, the same syntax I gave supports exactly that as well.