Strange behaviour of the Array type

Question

scala> List(1,2,3) == List(1,2,3)

res2: Boolean = true

scala> Map(1 -> "Olle") == Map(1 -> "Olle")

res3: Boolean = true

But when trying to do the same with Array, it does not work the same. Why?

scala> Array('a','b') == Array('a','b')

res4: Boolean = false

I have used 2.8.0.RC7 and 2.8.0.Beta1-prerelease.

Answer 1

Because the definition of "equals" for Arrays is that they refer to the same array.

This is consistent with Java's array equality, using Object.Equals, so it compares references.

If you want to check pairwise elements, then use sameElements

Array('a','b').sameElements(Array('a','b'))

or deepEquals, which has been deprecated in 2.8, so instead use:

Array('a','b').deep.equals(Array('a','b').deep)

There's a good Nabble discussion on array equality.