A different semantics for WeakMap#get default value

Mark S. Miller erights at google.com
Thu Jan 19 09:11:55 PST 2012

On Thu, Jan 19, 2012 at 12:00 AM, Andrea Giammarchi <
andrea.giammarchi at gmail.com> wrote:

> On Thu, Jan 19, 2012 at 7:51 AM, Mark S. Miller <erights at google.com>wrote:
>> Everyone on this thread, is there any need expressed in this thread that
>> is not satisfied by InfiniteMap?
> I would say for "notification purpose"
> result = lazyFactory(key, defaultValue);
> would be more appropriate

Hi Andrea, as I just mentioned in my reply to Andreas, I think this is a
good suggestion. However,

> otherwise the defaultValue looses completely its meaning the moment "key"
> is not there due the first if.

That's not quite true in the collection I posted, since an InfiniteMap is
only *initially* total. It still emulates deletes by using tombstones to
poke holes into its initially universal domain. When doing a get at a
deleted key, the defaultValue would come into effect.

> Out of curiosity, Chrome experimental flag does not support get(key,
> defaultValue) but get(key) only ... is this something missing or Map and
> WeakMap will never support officially the second get() argument?
> br

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