On 2006-05-16, at 13:08 EDT, John Sundman wrote:
> Excellent!
>
> jrs
>
> P.S. What's a "sentinel" ?
sentinel |ˈsentn-əl| |ˌsɛntn=əl| |ˌsɛntɪn(ə)l|
noun
a soldier or guard whose job is to stand and keep watch.
• figurative something that appears to be standing guard or keeping
watch.
• Medicine a thing that acts as an indicator of the presence of
disease : [as adj. ] the first national HIV sentinel surveillance
program in the developing world.
verb ( -neled, -neling; chiefly Brit. -nelled, -nelling) [ trans. ]
station a soldier or guard by (a place) to keep watch : a wide course
had been roped off and sentineled with police | figurative trees
sentineled the trenches.
PHRASES
stand sentinel (of a soldier) keep watch : soldiers stood sentinel
with their muskets | figurative a tall round tower standing sentinel
over the river.
ORIGIN late 16th cent.: from French sentinelle, from Italian
sentinella, of unknown origin.
In programming I use it to mean a 'thing that acts as an indicator'.
In this case, a value that is of the correct type (an event) but that
indicates that there isn't an event. As opposed to using `null`, a
sentinel is a valid member of the type with correct behavior.
> On May 16, 2006, at 1:03 PM, P T Withington wrote:
>
>> Henry and I are proposing:
>>
>> 1) Use a sentinel rather than null for declared events. This is
>> typesafe, will not crash Javascript, and can be optimized as
>> necessary.
>>
>> 2) setAttribute, which is the primary caller of sendEvent and
>> likely to be impacted performance-wise, will be re-written to be
>> careful about undeclared events and to not make function calls to
>> the sentinel event. (Safe, will not crash, can be optimized.)
>>
>> 3) The compiler will inline setAttribute and sendEvent. (It used
>> to inline setAttribute, that was turned off because it conflicted
>> with registers, is fairly easy to reintroduce. It should be easy
>> to inline enough of sendEvent to avoid unnecessary function calls.)
>>
>> On 2006-05-16, at 12:43 EDT, Jim Grandy wrote:
>>
>>> On May 16, 2006, at 7:42 AM, Amy Muntz wrote:
>>>
>>>> Task 2
>>>> Then, please use the DeclareEvent pattern, and remove the if's
>>>> as you no longer have to check for null. Please do this in the
>>>> same set of files you are currently working with, and then send
>>>> that out for review (Henry has volunteered to review this next
>>>> changeset - thanks, Henry!)
>>>
>>> Woah. The DeclareEvent isn't where the if's are -- it's in the
>>> sendEvent idiom we use. We'd need a SendEvent standalone function
>>> to get rid of the if's.
>>>
>>> SendEvent = function(evt, arg) {
>>> if (evt != null) evt.sendEvent(arg);
>>> }
>>>
>>> Then we can rewrite the body of SendEvent if the semantics change.
>>>
>>> Or am I confused? Can someone please write up a mini-proposal for
>>> what we're doing?
>>>
>>> Thanks,
>>>
>>> jim
>>
>
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