Prevent reassigning and mutating lifted objects

[ekeren]

Following #3064

It is now possible to capture reassignable/mutable objects
We need to prevent these captured object from being reassigned/modified in inflight

[Chriscbr]

example 1: Reassignment after a value has been lifted should be a compile time error

let var x = 1;

test "increment x" {
  x = x + 1;
  log("${x}");
}

example 2: Performing mutable operations after a value has been lifted should be a compile-time error

let arr = MutArray<num>[];

test "push item" {
  arr.push(123);
  log("${arr.length}");
}

example 3: These rules should also apply when operations are applied to members of classes

class Person {
  var name: str;
  pets: MutArray<str>;
  init() {
    this.name = "Bob";
    this.pets = MutArray<str>["whiskers", "fluffy"];
  }
  inflight changeName() {
    this.name = "Alice"; // error
  }
  inflight addPet(pet: str) {
    this.pets.push(pet); // error
  }
}

let person = new Person();

test "make changes" {
  person.pets.push("fido"); // error
  person.name = "Alice"; // error
}

[github-actions]

Hi,

This issue hasn't seen activity in 60 days. Therefore, we are marking this issue as stale for now. It will be closed after 7 days.
Feel free to re-open this issue when there's an update or relevant information to be added.
Thanks!

[Chriscbr]

Can we implement a mechanism in our type system so that when a mutable type defined in preflight is lifted into inflight, it is converted into its immutable variant? This would capture the idea that when a mutable collection is introduced to inflight, it gets "frozen" according whatever its last state in preflight was.

for example:

let x = MutArray<str>["hello", "world"];

inflight () => {
  let x0 = x.at(0); // "x" is type Array<str> in this context
  log(x0);
  x.push("!"); // error, since x is Array<str>
};

Inspired by #3174

[eladb]

Maybe, if an object has a lift(): T2 method, the compiler implicitly calls it and infers the types.

So now, we can implement shape shifting generically

[yoav-steinberg]

Note that inflight reassignment to a preflight variable part of this issue was handled in #3177, so we now have this compiler error:

class Person {
  pub var name: str;
  new() {
    this.name = "Bob";
  }
  inflight changeName() {
    this.name = "Alice"; // error: Variable cannot be reassigned from inflight
  }
}

let person = new Person();

test "make changes" {
  person.name = "Alice"; // error: Variable cannot be reassigned from inflight
}

[monadabot]

Congrats! 🚀 This was released in Wing 0.70.26.

[monadabot]

Congrats! 🚀 This was released in Wing 0.72.3.