this post was submitted on 17 Nov 2024
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Real Programmers Implement Functions On Top Of Classes (lemmy.sdf.org)
submitted 4 days ago by [email protected] to c/[email protected]
29 comments fedilink hide all child comments
 
class BaseFunction {
  static #allowInstantiation = false;

  constructor(...args) {
    if (!BaseFunction.#allowInstantiation) {
      throw new Error(
        "Why are you trying to use 'new'? Classes are so 2015! Use our fancy 'run' method instead!"
      );
    }
    for (const [name, validator] of this.parameters()) {
      this[name] = validator(args.shift());
    }
  }

  parameters() {
    return [];
  }

  body() {
    return undefined;
  }

  static run(...args) {
    BaseFunction.#allowInstantiation = true;
    const instance = new this(...args);
    BaseFunction.#allowInstantiation = false;
    return instance.body();
  }
}

class Add extends BaseFunction {
  parameters() {
    return [
      ["a", (x) => Number(x)],
      ["b", (x) => Number(x)],
    ];
  }

  body() {
    return this.a + this.b;
  }
}

console.log(Add.run(5, 3)); // 8
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[–] [email protected] 18 points 4 days ago (3 children)

It's just Java

[–] [email protected] 21 points 4 days ago* (last edited 4 days ago) (1 children)

Yep, some code examples from the official documentation. This:

printPersons(
    roster,
    (Person p) -> p.getGender() == Person.Sex.MALE
        && p.getAge() >= 18
        && p.getAge() <= 25
);

...is syntactic sugar for this:

interface CheckPerson {
    boolean test(Person p);
}

printPersons(
    roster,
    new CheckPerson() {
        public boolean test(Person p) {
            return p.getGender() == Person.Sex.MALE
                && p.getAge() >= 18
                && p.getAge() <= 25;
        }
    }
);

...which is syntactic sugar for this:

interface CheckPerson {
    boolean test(Person p);
}

class CheckPersonEligibleForSelectiveService implements CheckPerson {
    public boolean test(Person p) {
        return p.gender == Person.Sex.MALE &&
            p.getAge() >= 18 &&
            p.getAge() <= 25;
    }
}

printPersons(roster, new CheckPersonEligibleForSelectiveService());

The printPersons function looks like this:

public static void printPersons(List<Person> roster, CheckPerson tester) {
    for (Person p : roster) {
        if (tester.test(p)) {
            p.printPerson();
        }
    }
}

Basically, if you accept a parameter that implements an interface with only one method (CheckPerson), then your caller can provide you an object like that by using the lambda syntax from the first example.

They had to retrofit lambdas into the language, and they sure chose the one hammer that the language has.

Source: https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html

[–] [email protected] 14 points 4 days ago

That's not quite right. In bytecode, lambdas are significantly more efficient than anonymous class instances. So while the lambda implementation is semantically equivalent, characterizing it like you have is reductive and a bit misleading.

[–] [email protected] 4 points 4 days ago

Hence, Clojure. It's not just functions that implement IFn... as the string of "cannot cast to clojure.lang.IFn" errors that I get because I couldn't be bothered to validate my data's shape is eager to inform me.

[–] [email protected] 3 points 4 days ago* (last edited 4 days ago) (1 children)

Golang also does this, but it's not classes.

[–] [email protected] 1 points 4 days ago* (last edited 4 days ago) (1 children)

How so?

[–] [email protected] 1 points 4 days ago* (last edited 2 days ago) (1 children)

Golang uses modules, not classes. Each of which may have its own main function.

[–] [email protected] 1 points 3 days ago (1 children)

Huh? Main file? Do you mean main package? A module can contain an arbitrary number of main packages but I don’t see how that has anything to do with this post. Also are you saying modules are equivalent to classes? That may be the strangest take I’ve ever heard about Go.

[–] [email protected] 1 points 3 days ago

I meant main function. Oops