functional-decorators.md

Functional decorators

Disclaimer: random thoughts of mine; not sure if they are useful.

Motivating example

class StringBuilder {
  #data = '';
  proto add = logged @ function (str) {
    this.#data += str;
  };
  proto toString = logged @ function () {
    return this.#data;
  };
}

function logged(func) {
  return function (this, ...args) {
    console.log(args);
    return func.call(this, ...args);
  };
}

New constructs

• Prototype fields: proto key = value;

• Function application operator: f @ x === f(x)

  • Alternative: postfix use of decorators via pipeline operator:

    proto add = function (str) {
      this.#data += str;
    } |> logged;

• Optional this as an explicit parameter of universal functions:

  • Makes the use of this explicit in non-method functions.

Optional: this parameters for arrow functions

Turns arrow functions into methods:

class StringBuilder {
  #data = '';
  proto add = logged @ (this, str) => {
    this.#data += str;
  };
  proto toString = logged @ (this) => {
    return this.#data;
  };
}
function logged(func) {
  return (this, ...args) => {
    console.log(args);
    return func.call(this, ...args);
  };
}

Open questions

• Can logged() access the names of the methods? Would be useful for logging!