scala – HashSet和Set之间有什么区别,何时应该是每个

val defaultSet = Set("A","B")

HashSet是一个具体的实现,可以实例化如下：

val hashSet = HashSet("A","B")

看看“Scala中的编程”的引用,解释了各种实现之间的区别：

The scala.collection.mutable.Set() factory method,for example,
returns a scala.collection.mutable.HashSet,which uses a hash table
internally. Similarly,the scala.collection.mutable.Map() factory
returns a scala.collection.mutable.HashMap.

The story for immutable sets and maps is a bit more involved. The
class returned by the scala.collection.immutable.Set() factory method,
for example,depends on how many elements you pass to it,as shown in
the table below. For sets with fewer than five elements,a special class devoted exclusively to sets of each particular size is used,to maximize
performance. Once you request a set that has five or more elements in
it,however,the factory method will return an implementation that
uses hash tries.

Number of elements  Implementation
0                   scala.collection.immutable.EmptySet
1                   scala.collection.immutable.Set1
2                   scala.collection.immutable.Set2
3                   scala.collection.immutable.Set3
4                   scala.collection.immutable.Set4
5 or more           scala.collection.immutable.HashSet

这意味着对于具有5个或更多元素的不可变集合,您的两个调用都应该返回同一个Set子类的实例.

地图同样如此.请参阅this链接.