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The mutable Set has a method def +=(elem1: A, elem2: A, elems: A*): Set.this.type but I can call this method with a single paramter:
val s = scala.collection.mutable.Set(1, 2)
s += 4
What method is actually called? There seems to be no overload for += with a single parameter. What is the intention of the above method signature?
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The effect of = can also be used to easily understand what ++= would do. Since ++ generally represents concatenation of two collections, ++= would mean an "in place" update of a collection with another collection by concatenating the second collection to the first.
A set is a collection which only contains unique items which are not repeatable and a list is a collection which contains immutable data. In scala, ListSet class implements immutable sets using a list-based data structure.
In Java and Scala, certain builtin (a/k/a primitive) types get passed-by-value (e.g. int or Int) automatically, and every user defined type is passed-by-reference (i.e. must manually copy them to pass only their value).
Well, a little investigation here:
scala> val s = scala.collection.mutable.Set(1,2)
s: scala.collection.mutable.Set[Int] = Set(1, 2)
scala> s += 4
res0: s.type = Set(1, 2, 4)
scala> s +=
<console>:9: error: missing arguments for method += in trait SetLike;
follow this method with `_' if you want to treat it as a partially applied funct
ion
s +=
^
Oh, OK, so let's find the trait SetLike docs:
abstract def +=(elem: A): SetLike.this.type
Adds a single element to the set.
And now it's clear it's an implementation of an abstract method in the mutable.SetLike trait.
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