On Mar 21, 2011, at 1:13 PM, Erik Arvidsson wrote:
>
> The above use case cannot be solved using private names because
> private names conflict with public names.
>
Erik, I'm not sure that my understanding of the intended semantics of your
extension statement is totally correct. But given what I I think you intended
here is how I might imagine it desugaring using private names. Let me know
what I misinterpretered:
{
private filter;
Object.prototype.filter = function(fun) {
var publicFilter= this["filter"];
if (publicFilter) return publicFilter.apply(this,arguments);
var retval = {};
for (var key in this) {
if (fun(this[key])
retval[key] = this[key];
}
return retval;
}
function largerThanN(obj, n) {
return obj.filter(function(item) {
return item > n;
}
}
var a = [0, 1, 2, 3, 4];
print(largerThanN(a, 2));
var o = {a: 0, b: 1, c: 2, d: 3, e: 4};
print(largerThanN(0, 2));
delete Object.prototype.filter
}
On Mar 21, 2011, at 1:13 PM, Erik Arvidsson wrote:
> The thread about using private names is getting a bit unwieldy but I'd
> like to focus on the use case that I have been thinking of as
> "Lexically scoped monkey patching" or "Lexically scoped object
> extensions" instead of focusing on how to use "private names" to fit
> this scenario.
>
> Extending built ins and modifying existing classes to work around bugs
> or to provide a better API is (or was) a common pattern. Today a lot
> of JS library shun this approach due to the risk of conflicts.
>
> Let us assume that you could extend an object in your current lexical
> scope and that such extensions could be imported from a module into
> your current scope.
>
> Given:
>
> {
> function largerThanN(obj, n) {
> return obj.filter(function(item) {
> return item > n;
> }
> }
>
> var a = [0, 1, 2, 3, 4];
> print(largerThanN(a, 2));
> }
>
> Now we would like to make largerThanN to work with Object objects. The
> naïve thing to do is to just to add a filter method to
> Object.prototype. However, this might cause conflicts with other code
> that uses objects. The idea here is that we can do this safely in our
> scope (ignore syntax except that it is important that it can be done
> statically).
>
> {
> extend Object.prototype with {
> filter: function(fun) {
> var retval = {};
> for (var key in this) {
> if (fun(this[key])
> retval[key] = this[key];
> }
> return retval;
> }
> };
>
> function largerThanN(obj, n) {
> return obj.filter(function(item) {
> return item > n;
> }
> }
>
> var a = [0, 1, 2, 3, 4];
> print(largerThanN(a, 2));
> var o = {a: 0, b: 1, c: 2, d: 3, e: 4};
> print(largerThanN(0, 2));
> }
>
> The above use case cannot be solved using private names because
> private names conflict with public names.
>
> Can we agree that this is a use case that we care about and focus on
> this instead of whether private names can or cannot do this?
>
> --
> erik
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