Do not compare arrays with ==

When comparing two arrays for equality, use sameElements rather than ==.


== does not compare arrays for value equality, but for reference equality.

This gives us the following counter-intuitive behaviour:

Array(1) == Array(1)
// res0: Boolean = false

This is because Array is essentially an alias for Java’s array, which implements equals as reference equality - only returning true if two variables point to the same array instance.

sameElements, on the other hand, has the behaviour you’d expect:

Array(1) sameElements Array(1)
// res1: Boolean = true


An alternative to sameElements is calling deep on each array before comparison:

Array(1).deep == Array(1).deep
// res2: Boolean = true

This is not the preferred solution because it’s slightly more expensive, creating instances that will be discarded immediately.

Checked by

  • ArrayEquals