On Jun 23, 2011, at 12:31 PM, Axel Rauschmayer wrote:
>> This is entirely beside the point.
>>
>> Dynamic |super| as Sean proposes requires *every call site* to pass the
>> |here| parameter or something derived from it, no way around that.
>>
>> Paying for 'super' if you use it, buying by the yard, is not a problem.
>>
>> Making *every function call* in the language slow, increasing register
>> pressure, etc. -- absent aggressive inference to identify callees and
>> specialize call sites to them (inlining VMs do this but it can backfire, so
>> there will be a default case that can't do this) -- is a big problem.
>
> I believe you about the dynamic super. I can summarize my question as follows:
> - Making "super" or "current object" available to a function incurs costs.
If it is statically bound (via a [[Super]] or [[Current]] internal property
then there is only a cost (and a small one) on actual accesses of super. EG,
Object.defineMethod(obj,'foo", function() {return super.foo() /*cost to
access [[Super]] + cost to access this */});
If dynamically bound (on each property lookup of the method) then there is a
cost on every function call to pass the current object reference to the
function invocation. This cost is in addition to the const of passing thethis
reference.
> - Making "current function" available to a function does not incur costs?
> This is *not* an extra parameter, then?
the current function is made available via the function name in a function
declaration:
var q= -1;
Object.defineMethod(obj"foo",function bar(a,b,c) {return q*bar.length /*
returns -3 */});
bar is a lexically scoped binding just like q. No per call perimeters are
involved. The cost to access bar is approximately the same as the cost of
accessing q (exact costs subject to details of how lexically scoped access is
implemented)
Allen
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