> - One key question: Does a property declaration have to look declarative in > order to be used declaratively? You are saying no. > > I think a more declarative form could be added later, this is not future > hostile to that.
It looks OK to me. However, adding another form later seems like a bad idea. > What is currently here makes it so that any properties added during > construction are non-configurable. Assuming the constructor gets run, and > assuming properties are not added conditionally, guarantees can be made. Wouldn’t the instance be frozen? Then all properties would be non-configurable and non-writeable and the instance would not be extensible. > - One could have `public foo = ...` as syntactic sugar for `this.foo = ...`. > But then the issue is whether `private` will ever be used in an analogous > manner (my understanding: no). > > Going with the max/min approach of tiny additions. The only addition here is > the const keyword in front of class. Big bang for the buck. I agree. > - Subtyping is going to be a bit tricky, because a constructor has to behave > differently if called from a subconstructor. > > This is covered in the original proposal, and I would have it work the same: > "During construction of an instance of a const class, the instance is > extensible. Each public declaration adds a non-configurable, (possibly > non-writable) data property to the instance. During constructor chaining, the > [[Call]] method of the superclass constructor, even if const, does not make > the instance non-extensible. Rather, the [[Construct]] method of a const > class makes the instance non-extensible before returning. An instance of a > non-const class which inherits from a const class is thereby born extensible > unless the constructor makes it non-extensible by other means. Taken > together, instantiating a const class must result either in a thrown > exception, non-termination, or in an instance of that class with the public > own properties declared within the constructor of that class." Nice. But it goes beyond a class declaration being syntactic sugar for a function (unless one introduces a way to specify [[Construct]]). > - I would love to have sealed instances. Those would be great for catching > typos and performing shape-related optimizations. > > Yes, I think I might have specified this poorly. I'm seeking the same > behavior as the original const class proposal. Instances would be > non-extensible upon completion of construction. Nothing could be added or > removed. Methods would be non-writable, but data would be. As I indicated, > private names can be used to protect against unwanted mutation. What function (or equivalent operation) would [[Construct]] apply to an instance after initialization? Object.seal() or Object.freeze()? -- Dr. Axel Rauschmayer [email protected] home: rauschma.de twitter: twitter.com/rauschma blog: 2ality.com
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