gibson042
commented
2 years ago myMap.set(myMap.getOr(key, 0), value + 1) only implements upsert if getOr(key, defaultValue) returns key, which seems rather pointless.
But regardless, note that the README identifies distinct scenarios and that each of them potentially mutate the map:
- set [initial] value if key is absent:
const value = map.emplace(key, { insert: ()=>defaultValue }) - update value if key is present:
const value = map.emplace(key, { update: oldValue=>{…} }) - set initial or updated value (combination of the preceding):
const value = map.emplace(key, { insert: ()=>initialValue, update: oldValue=>{…} })
Getting a possibly-default value without mutating the map would be an expansion of scope, albeit potentially an appropriate one. But not at the expense of the above scenarios in either behavior or comprehensibility (probably ruling out something like const value = map.emplace(key, { skipInsert: ()=>defaultValue }) unless the priority of insert vs. skipInsert can be made obvious).
conartist6
papb
The most common problem in
Mapusage is the one this proposal doesn't address.myMap.has(key) ? myMap.get(key) : nonestill isn't sufficiently safe or static. Class extension can break it. Typescript can't handle it. Flow can't handle itWhat if the API was simply:
Then upsert becomes:
myMap.set(myMap.getOr(key, 0), value + 1);