this post was submitted on 17 Nov 2024
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Real Programmers Implement Functions On Top Of Classes (lemmy.sdf.org)
submitted 9 hours ago by [email protected] to c/[email protected]
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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] 8 points 8 hours ago (2 children)

It's just Java

[–] [email protected] 6 points 4 hours ago* (last edited 4 hours ago)

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] 2 points 5 hours ago* (last edited 5 hours ago)

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