On Jul 10, 2011, at 3:02 PM, David Herman wrote: >>> I'm not sure what Array.prototype methods would or wouldn't work on >>> instances of SubArray. >> >> All of them. They are all generic. > > We're speaking too broadly here. It depends on what we want to work how. For > example, .map can't magically know how to produce a SubArray as its result if > that's how SubArray wants it to work. But what I'm actually more concerned > about is the behavior of .length. Does the <| semantics make .length work > automagically the way it does for ordinary Array instances?
Of course, since the thing on the right of <| is a newly minted Array which has its own length. There's no issue here -- are you thinking of the other case (which I showed), Object.create([])? That's where length doesn't "inherit". >> However, subarray instances have all the internal state and methods that >> make them true arrays so even if some of the inherited Array methods weren't >> generic they would still work. > > Including .length (which isn't a method, but YKWIM)? The <| operator sets [[Prototype]] in the newborn-because-literally-expressions right operand, to the value of the left operand. So (proto <| [1,2,3]) is an Array instance, no mystery or inheritance of Arrayness required. The trick as your SubArray example showed is not to lose the Array.prototype heritage -- proto ought to have Array.prototype on its proto-chain. 'length' is own in each Array instance, maintained by [[Put]] in ES1-3, [[DefineOwnProperty]] in ES5. /be _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
