immutable maps have a dangerous remove method

[Ichoran]

Immutable maps have a new method called remove that is dangerous when combined with mutable maps which have a side-effecting remove. If you get your map type wrong, you will silently fail to modify your map with no error.

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scala> val m = Map(3 -> "wish")
m: scala.collection.immutable.Map[Int,String] = Map(3 -> wish)

scala> m.remove(3)
res0: scala.collection.immutable.Map[Int,String] = Map()

scala> val mm = collection.mutable.Map(3 -> "wish")
mm: scala.collection.mutable.Map[Int,String] = HashMap(3 -> wish)

scala> mm.remove(3)
res1: Option[String] = Some(wish)

scala> mm
res2: scala.collection.mutable.Map[Int,String] = HashMap()

Immutable maps cannot have a remove method since the mutable map return value will often be ignored and hence the different return types cannot be used to catch the error.

[exoego]

Related issue #10939

Shoud we deprecate immutable.Map#remove and add alias updatedremoved, as similar as immutable.Map#updated vs mutable.Map#update ?

If immutable.Map.remove is deprecated, users are able to get compiler warning about dangerous ignoring return value of the method.

[yhpark]

@exoego you mean add alias removed?

[exoego]

@yhpark Ah, yes,thank you. Corrected my comment.

[szeiger]

No need to deprecate, the method didn't exist yet in 2.12.

[szeiger]

There's also removeAll which needs to be renamed to removedAll. This method is also found in immutable.Set (where the remove-single-item method is called excl).

[som-snytt]

I haven't followed new collections, apologies for the brief incursion. This is like not knowing if += is a method that updates. That is what lint rules are for, in this case, to warn if the result is not used. The name removed is slightly awkward; it is shorter than havingRemoved(x).

[Ichoran]

It follows the form of other methods (past tense is immutable), but I agree that it's clunky. I wasn't able to think of a better alternative.

[joshlemer]

(throwing out ideas) minusAll ?

[som-snytt]

I apologize again for stripping the paint off the bike shed.

[szeiger]

I expect the names will be mostly used for implementing collections. Users will continue to use -. The difference in the new collections is that all symbolic methods also have a proper alphabetic name.