On Oct 17, 2011, at 5:18 PM, David Herman wrote:
> I suspect it's not nearly so rare as you think. For example, it just showed
> up in Tom and Mark's new proxy proposal:
>
>> The protect trap is called on
>> Object.{freeze,seal,preventExtensions}(aProxy). The operation argument is a
>> string identifying the corresponding operation (“freeze”, “seal”,
>> “preventExtensions”). This makes it easy for a handler to forward this
>> operation, by e.g. performing Object[operation](obj).
>
>
> A simple way to abstract out "do this concrete operation" to "do one of the
> following set of possible concrete operations" is to pass the name as a
> string. Yes, there's a certain aesthetic that says that's icky, but JS makes
> it so convenient that it's the obvious thing to do.
JS libraries are full of computed method name calls. It's quite common.
http://codesearch.google.com/#search/&q=%22%5D(%22%20lang:js&type=cs
/be
>
> Dave
>
> On Oct 17, 2011, at 4:15 PM, Allen Wirfs-Brock wrote:
>
>>
>> On Oct 17, 2011, at 3:34 PM, David Herman wrote:
>>>
>>>
>>>> IMHO the single "property name space" of es-current is a feature, not a
>>>> bug.
>>>
>>> I tend to agree. There are expressibility problems, too. For example, if
>>> you have an object that uses . for its API and [] for some other data, then
>>> what do you do when you want to dynamically compute an API name?
>>
>> In most languages, this would fall into the realm of the reflection API.
>>
>> What is the actual frequency of such driven API member selection. If it is
>> high (particularly, high than the utility of good collections) that we may
>> be exposing other problems we need to look at more closely.
>>
>>
>>> I would hope not
>>>
>>> eval("obj." + computeName())
>>>
>>> But I don't see any obvious ways out of this that aren't pretty convoluted.
>>>
>>
>> I'll give you four:
>>
>> 1) Object.getOwnPropertyDescriptor(obj,name).value
>> etc.
>>
>> 2) two new reflection functions:
>> Object.getProperty(obj,name)
>> Object.setProperty(obj,name,value)
>>
>> 3) build upon the possible alternative private name property syntax
>> let foo='foo';
>> obj@foo
>> or perhaps
>> obj@('foo')
>>
>> 4) a switch statement:
>> switch (computedAPIName) {
>> case 'property1':
>> obj.property1(/*args */);
>> break;
>> case 'property2':
>> obj.property2(/*args */);
>> break;
>> case 'property3':
>> // etc.
>> }
>>
>> All of these start from the perspective that this sort of reflective API
>> access should be quite rare.
>>
>> Allen
>>
>>
>>
>>
>>
>
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