Say I have an Array[Int]
like
val array = Array( 1, 2, 3 )
Now I would like to append an element to the array, say the value 4
, as in the following example:
val array2 = array + 4 // will not compile
I can of course use System.arraycopy()
and do this on my own, but there must be a Scala library function for this, which I simply could not find. Thanks for any pointers!
Notes:
I am aware that I can append another Array of elements, like in the following line, but that seems too round-about:
val array2b = array ++ Array( 4 ) // this works
I am aware of the advantages and drawbacks of List vs Array and here I am for various reasons specifically interested in extending an Array.
Thanks for the answers pointing to the :+
operator method. This is what I was looking for. Unfortunately, it is rather slower than a custom append() method implementation using arraycopy
-- about two to three times slower. Looking at the implementation in SeqLike[]
, a builder is created, then the array is added to it, then the append is done via the builder, then the builder is rendered. Not a good implementation for arrays. I did a quick benchmark comparing the two methods, looking at the fastest time out of ten cycles. Doing 10 million repetitions of a single-item append to an 8-element array instance of some class Foo
takes 3.1 sec with :+
and 1.7 sec with a simple append()
method that uses System.arraycopy();
doing 10 million single-item append repetitions on 8-element arrays of Long takes 2.1 sec with :+
and 0.78 sec with the simple append()
method. Wonder if this couldn't be fixed in the library with a custom implementation for Array
?
For what it's worth, I filed a ticket: https://issues.scala-lang.org/browse/SI-5017
You can use :+
to append element to array and +:
to prepend it:
0 +: array :+ 4
should produce:
res3: Array[Int] = Array(0, 1, 2, 3, 4)
It's the same as with any other implementation of Seq
.