Allen Wirfs-Brock wrote:
On Jan 17, 2012, at 3:45 AM, Herby Vojčík wrote:
Brendan Eich wrote:
Clearly(!) a set-if-not-present method should not be misnamed
"get".
I like the optional sentinel-meaning-not-found for get, and
setDefault per Python as Tab pointed out. Agree they should not
be merged into one API. Bikeshedding setDefault at leisure (in
background in my head ;-).
Like: getIfAbsentSet(key, dflt) with dflt being mandatory? Still
there is question of laziness of dflt, the original
#get:ifAbsentPut: has the block as its second argument.
The Smalltalk solution to this problem is the at: key ifAbsent:
block method.
There is also
at: key ifAbsentPut: block
At least in Squeak it was there.
This subsumes both get with default value and get create if missing
use cases plus others. In JS we might say:
col.getIfAbsent(key) {|| 42}; //use 42 if no present
col.getIfAbsent(key) {|| col.defaultValue}; //have collection
provide the default value
col.getIfAbsent(key) {|| col.put(key, 42); 42} //if key isn't there
add it with an appropriate vaue
except it computes collection twice. If it is something like:
foo.bar().getIfAbsent(key) {|| foo.bar().put(key, 42); 42}
it is a bit clumsy. You can pass the collection itself in an argument
foo.bar().getIfAbsent(key) {|c| c.put(key, 42); 42}
but you have the same problem with value, if it is computed, you must
foo.bar().getIfAbsent(key) {|c| let v = baz(); c.put(key, v); v}
so it seems better to have different api and write
foo.bar().getIfAbsentSet(key) {|| baz()}
Also, Mark S. Miller wrote:
As it is now, I can give someone a read-only view of a WeakMap wm my
simply giving them
{ get: wm.get.bind(wm), has: wm.has.bind(wm) }
so distinct API is for writeback version is probably not a bad idea.
Allen
Herby
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