The Private Names strawman currently combines a new runtime capability (using
both strings and private names as keys in objects) with several new syntactic
constructs (private binding declarations, #.id). At the March meeting, I
recall there was some support for the idea of separating these two aspects, and
exposing the runtime capability also as a library that could be used in
'text/javascript'.
I added a comment to the Private Names strawman page to suggest how this could
be done. The runtime behavior of the proposal is the same, but in addition, a
library function "Object.createPrivteName(name)" is added which provides direct
access to the internal CreatePrivateName abstract operation. This allows the
use of private names in a more verbose form, but without needing new syntax -
similar in spirit to the ES5 Object.* operations.
Borrowing an example from the current proposal to illustrate:
Using 'text/harmony' syntax:
function Point(x,y) {
private x, y;
this.x = x;
this.y = y;
//... methods that use private x and y properties
}
var pt = new Point(1,2);
Using 'text/javascript' syntax:
function Point(x,y) {
var _x = Object.createPrivateName("x");
var _y = Object.createPrivateName("y");
this[_x] = x;
this[_y] = y;
//... methods that use private _x and _y properties
}
var pt = new Point(1,2);
There seem to be several benefits to this:
(1) The private name capability can be made available to 'text/javascript'
(2) The feature is easily feature-detectable, with a fallback of using
'_'-prefixed or similar pseudo-private conventions
(3) The core functionality can potentially be agreed upon and implemented in
engines earlier than full new syntax
Luke
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