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Clarify behaviour of private fields #90

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dmitriid opened this issue Jun 8, 2017 · 7 comments
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Clarify behaviour of private fields #90

dmitriid opened this issue Jun 8, 2017 · 7 comments

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@dmitriid
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dmitriid commented Jun 8, 2017

Based on https://medium.com/the-thinkmill/javascripts-new-private-class-fields-93106e37647a

class Point {
  #x;
  #y;
  
  constructor(x, y) {
    this.#x = x;
    this.#y = y;
  }
  equals(other) {
    return this.#x === other.#x && this.#y === other.#y;
  }
}

The code for equals breaks assumptions about private fields. A private field is expected to be instance-private and non-accessible anywhere.

It looks like if a method happens to be in class A and and arbitrary variable happens to be of type A, then the method can access the variable's private fields at a whim.
@littledan
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This proposal was designed with class-private, rather than instance-private, semantics as a goal. Many other programming languages operate this way. What drives the expectation that it be instance-private for you?

@dmitriid
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dmitriid commented Jun 8, 2017

It was my feeling that most popular languages have instance-private fields. Now I realise it's more of a 50-50-ish split :)

@bakkot
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bakkot commented Jun 8, 2017

Out of curiosity, what languages have instance-private fields? Off the top of my head I can't think of one - C++, Java, Python, PHP, Swift, TypeScript, etc all have some notion of a class with a private field, and in all of them it's class-private or something even less restrictive.

@littledan
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Maybe Ruby?

@ljharb
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ljharb commented Jun 8, 2017

(fwiw, in Ruby, nothing is hard-private due to .send)

@dmitriid
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dmitriid commented Jun 9, 2017

Argh. Look slike I've spent too much time in languages which have modules instead of classes and I forgot all about privates :)

@littledan
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OK, let's stick with class-private then.

@bakkot bakkot mentioned this issue Aug 3, 2017
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@loganfsmyth loganfsmyth mentioned this issue Nov 6, 2017
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4 participants
@dmitriid @ljharb @littledan @bakkot