Add lazy function

[aleclarson]

Define a property whose value isn't calculated until first access.

lazy(obj, 'key', () => expensiveCalculation())

obj.key // calculates the value on-demand
obj.key // returns a cached result on future access

// use `this` to access other properties
lazy(obj, 'key', function() {
  return expensiveCalculation(this.otherKey)
})

It can also be used as a decorator.

class MyClass {
  @lazy get thing() {
    return expensiveCalculation(this)
  }
}

[Minhir]

It can be easily solved with once:

class MyClass {
  get thing() {
    return once(expensiveCalculation);
  }
}

[aleclarson]

I think you mean this?

class MyClass {
  getThing = once(expensiveCalculation.bind(this));
}

But yeah, probably best to avoid having multiple ways to accomplish the same thing. There's a downside in terms of stylistic preference, but that's not really a good enough justification. Arguably, keeping “expensive calculations” as functions is better anyway, since basic property access is often assumed to be cheap. Also, using once gives you support for once.reset, allowing you to clear the memoization.

Overall, I concur that this proposal should be rejected!