How I can use another way to copy a Array to another Array?
My thought is to use the = operator. For example:
val A = Array(...)
val B = A
But this is okay?
Second way is to use for loop, for example:
val A = Array(...)
val B = new Array[](A.length)//here suppose the Type is same with A
for(i <- 0 until A.length)
B(i) = A(i)
You can use .clone
scala> Array(1,2,3,4)
res0: Array[Int] = Array(1, 2, 3, 4)
scala> res0.clone
res1: Array[Int] = Array(1, 2, 3, 4)
The shortest and an idiomatic way would be to use map with identity like this:
scala> val a = Array(1,2,3,4,5)
a: Array[Int] = Array(1, 2, 3, 4, 5)
Make a copy
scala> val b = a map(identity)
b: Array[Int] = Array(1, 2, 3, 4, 5)
Modify copy
scala> b(0) = 6
They seem different
scala> a == b
res8: Boolean = false
And they are different
scala> a
res9: Array[Int] = Array(1, 2, 3, 4, 5)
scala> b
res10: Array[Int] = Array(6, 2, 3, 4, 5)
This copy would work with all collection types, not just Array.
Consider Array.copy in this example where dest is a mutable Array,
val a = (1 to 5).toArray
val dest = new Array[Int](a.size)
and so
dest
Array[Int] = Array(0, 0, 0, 0, 0)
Then for
Array.copy(a, 0, dest, 0, a.size)
we have that
dest
Array[Int] = Array(1, 2, 3, 4, 5)
From Scala Array API note Scala Array.copy is equivalent to Java System.arraycopy, with support for polymorphic arrays.
Another option is to create the new array, B, using A as a variable argument sequence:
val B = Array(A: _*)
The important thing to note is that using the equal operator, C = A, results in C pointing to the original array, A. That means changing C will change A:
scala> val A = Array(1, 2, 3, 4)
A: Array[Int] = Array(1, 2, 3, 4)
scala> val B = Array(A: _*)
B: Array[Int] = Array(1, 2, 3, 4)
scala> val C = A
C: Array[Int] = Array(1, 2, 3, 4)
scala> B(0) = 9
scala> A
res1: Array[Int] = Array(1, 2, 3, 4)
scala> B
res2: Array[Int] = Array(9, 2, 3, 4)
scala> C(0) = 8
scala> C
res4: Array[Int] = Array(8, 2, 3, 4)
scala> A
res5: Array[Int] = Array(8, 2, 3, 4)
