When checking whether a collection is empty, use
isEmpty
ornonEmpty
rather than the all too commonsize == 0
.
Collections such as List
require a complete traversal to compute their size. Doing so just to check whether there’s at least one element is clearly more expensive than it needs to be.
To prove this point, let’s create a simple benchmarking method:
def time[A](t: => A): Long = {
val now = System.currentTimeMillis()
t
System.currentTimeMillis()  now
}
We’ll also need an unreasonably large List
:
val list = (0 to 10000000).toList
We can now check that one approach is indeed far longer than the other:
time(list.isEmpty)
// res0: Long = 0L
time(list.size == 0)
// res1: Long = 36L
Some collections are infinite, and will loop forever when you try to compute their length:
// Don't run this.
Stream.from(1).size
isEmpty
, on the other hand, behaves sanely:
Stream.from(1).isEmpty
// res2: Boolean = false
Linter  Rule 

Scapegoat 
