Scala: what is the best way to append an element to an Array?

问题

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.

Edit 1

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?

Edit 2

For what it's worth, I filed a ticket: https://issues.scala-lang.org/browse/SI-5017

回答1:

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.

回答2:

val array2 = array :+ 4
//Array(1, 2, 3, 4)

Works also "reversed":

val array2 = 4 +: array
Array(4, 1, 2, 3)

There is also an "in-place" version:

var array = Array( 1, 2, 3 )
array +:= 4
//Array(4, 1, 2, 3)
array :+= 0
//Array(4, 1, 2, 3, 0)

回答3:

The easiest might be:

Array(1, 2, 3) :+ 4

Actually, Array can be implcitly transformed in a WrappedArray

来源：https://stackoverflow.com/questions/7500081/scala-what-is-the-best-way-to-append-an-element-to-an-array

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arrays

scala

append