Will values in function generate every time? - scala

Question

object isValidUuid {
val sample = "f40473b8-9924-2a9a-bd82-7432191f2a75"
val len = sample.length
val dashIndices = sample.indices.filter(sample(_) == '-')
def apply(string: String) = {
string.length == len && dashIndices.forall(string(_) == '-')
}
}
def isValidUuid(string: String) = {
//f40473b8-9924-2a9a-bd82-7432191f2a75
val sample = "f40473b8-9924-2a9a-bd82-7432191f2a75"
val len = sample.length
val dashIndices = sample.indices.filter(sample(_) == '-')
string.length == len && dashIndices.forall(string(_) == '-')
}
Did the object and function isValidUuid do exactly the same thing,
or object will be faster,because function calculate len and dashIndices every time?

Answer 1

This scala code:
object O {
val i = 1
def foo = {
i
}
def bar = {
val x = 1
x
}
}
Compiles to this java:
public class _$$anon$1$O$ {
private final int i;
public int i() {
return this.i;
}
public int foo() {
return this.i();
}
public int bar() {
final int x = 1;
return x;
}
{
this.i = 1;
}
}
// lazy object initialization omitted
As you can see, all values inside the function are transpiled into local variables, while values inside the object are class fields and they are initialized only once (when object is initialized). I omitted object initialization code for clarity.
Check my scala-to-java tool, it helps to understand how scala works in such cases.

Answer 2

You can easy test this, adding sleep to your lenght calculation
object isValidUuidObj {
val sample = "f40473b8-9924-2a9a-bd82-7432191f2a75"
val len = {
Thread.sleep(1000)
sample.length
}
val dashIndices = sample.indices.filter(sample(_) == '-')
def apply(string: String) = {
string.length == len && dashIndices.forall(string(_) == '-')
}
}
def isValidUuid(string: String) = {
//f40473b8-9924-2a9a-bd82-7432191f2a75
val sample = "f40473b8-9924-2a9a-bd82-7432191f2a75"
val len = {
Thread.sleep(1000)
sample.length
}
val dashIndices = sample.indices.filter(sample(_) == '-')
string.length == len && dashIndices.forall(string(_) == '-')
}
Yes, object will be faster, but I don't think that in your case this difference is important.
You'd better keep all constants in object (magic numbers/strings are always bad idea), while using object for calculations is not a clean solution.