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▲ zelphirkalt 2 days ago

The visitor pattern is my go to example for patterns, that you don't really need, when you have a language that has first class functions, which implies among other things, that you can pass functions as arguments, like you can pass anything else.

The magical "visitor" pattern becomes nothing more than simple callback passing or passing a function, which is one of the most natural things to do in a modern programming language.

State machines at least are useful as a conceptual thing, to find a way to think about how one solves a problem, no matter how they are ultimately implemented in the end.

▲vips7L 2 days ago | parent [-]

I've always seen the visitor pattern as a poor-mans pattern matching. How do you solve the same thing with callbacks?

▲zelphirkalt 2 days ago | parent [-]

Instead of defining a Visitor interface and then making objects to implement the interface and then passing those objects to whatever traverses a graph or iterates through something, you pass the function, that will be called, by whatever traverses a graph or iterates through something.

▲vips7L a day ago | parent [-]

Kind of like how sum types and matching are implemented in library code? Example from D here:

    Fahrenheit toFahrenheit(Temperature t)
    {
        return Fahrenheit(
            t.match!(
                (Fahrenheit f) => f.degrees,
                (Celsius c) => c.degrees * 9.0/5 + 32,
                (Kelvin k) => k.degrees * 9.0/5 - 459.4
            )
        );
    }