One probably should separate two concerns: providing a default value vs. adding
missing values to the collection.
One possible signature:
function get(key, default = undefined, addIfMissing = false)
The above would also allow you to store `undefined` and detect missing values,
by using a special value (e.g. named NO_VALUE) as the default.
On Jan 16, 2012, at 21:09 , David Bruant wrote:
> Hi,
>
> I recently wrote some code using WeakMaps and the following pattern
> keeps coming over and over:
> -----
> var v = wm.get(o);
> if(v === undefined){
> v = someValue;
> order.set(o, v);
> }
>
> // now, wn has a value for o (either it already did or it's been added)
> // v === wm.get(o)
> // play with v
> -----
>
> The "v === undefined" is fine in my case, because I know I never store
> "undefined" as a value.
>
> I thought that maybe the semantics of WeakMap#get could be changed
> whenever the key is not used to set the value and return it.
> My pattern would be reduced to:
> -----
> var v = wm.get(o, someValue);
> // now, wn has a value for o (either it already did or it's been added)
> // v === wm.get(o)
> // play with v
> -----
>
> Thinking more about the current semantics, I thought that what is
> currently done could be achieved a bit differently:
> -----
> var v = wm.get(o, def);
> // almost equivalent to:
> var v = wm.get(o) || def;
> -----
> There is a difference when the vaue stored in the weak map is a falsy value.
>
> My personal experience is to store mostly objects (so truthy) as weak
> map values, so I wouldn't be affected. Has anyone else experience in
> storing falsy values?
>
> David
> _______________________________________________
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>
--
Dr. Axel Rauschmayer
[email protected]
home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com
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