@ operator

at_operator.js

// Based on: http://wiki.ecmascript.org/doku.php?id=strawman:syntactic_support_for_private_names

//// The at (@) operator

// Intuitively:
// - obj.@foo is syntactic sugar for obj[foo]
// - @foo is syntactic sugar for [foo] (for method definitions, property definitions, etc.)


// Usage: Let propName be a normal variable holding either a symbol or a string.
// - Property access: obj.@propName
// - Property definition (object literal): @propName: propValue
// - Method definition (class, object literal): @propName(...) { ... }
// - Getter definition (class, object literal): get @propName() { ... }
// - Setter definition (class, object literal): set @propName(x) { ... }
// - Generator method definition (class, object literal): *@propName(x) { ... }

//// Declare symbols (e.g.):

public myPublicSymbol; // or `name` or `symbol`
// Equivalent: let myPublicSymbol = new Name(true)
private myPrivateSymbol;
// Equivalent: let myPrivateSymbol = new Name()

// optional: class-internal declarations and other features proposed by Allen

//// Example: object literal

private foo, bar, baz, bam;
let obj = {
    @foo: "a data property",
    @bar() {return "a concise method property"},
    get @baz() {return "a get accessor"},
    *@bam(n) {yield 0; return n} //a generator method
};
console.log(obj.@foo);  // a data property

//// Example: classes

private x, y;
public validate;

class Point {
   get x() {return this.@x}
   set x(v) {this.@x = this.@validate(v)}
   get y() {return this.@y}
   set y(v) {this.@y = this.@validate(v)}
   @validate(value) {
      if (typeof value !== "number") throw TypeError("number expected");
      return value;
   }
   constructor (x,y) {
      this.x = x;
      this.y = y;
   }
};
 
class QIPoint extends Point{
   @validate(value) {
      super.@validate(value);
      if (value<0) throw RangeError("negative values not accepted");
      return value;
   }
}