20190316 Multiple Assignments

I stumbled over this problem when writing code in Groovy, where I return a tuple from a function.

You can access the single values of the tuple by destructuring it, but Intellij Idea will inform you about unused variables if you don’t use all values of the tuple.

I wanted to know if there is a way to receive only parts of the tuple.

I still learn how this works.

While writing the code examples I understood I also have to check and compare which languages support tuples with mixed types…

Groovy

You can return tuples from functions :

def f() {
  return [1,2,3]
}

def (a, b, c) = f()

assert a == 1
println a

assert b == 2
println b

assert c == 3
println c

My problem was : Do I have to create unused variables if I don’t need the complete tuple?

The answer is : Yes, you cannot omit receiving single variables, the underscore is only a fake, it is a real variable and Intellij Idea still warns me the underscore is unused if I comment out the last two lines :

def f() {
  return [1,2,3]
}

def (d, _, e) = f()

assert d == 1
println d

assert e == 3
println e

assert _ == 2
println _

Swift

Here it works with the underscore, you cannot compile print(_) :

func f() -> (Int, Int, Int){
    return (1,2,3)
}

let (a,b,c) = f()

assert (a == 1, "error : a")
print(a)

assert (b == 2, "error : b")
print(b)

assert (c == 3, "error : c")
print(c)

let (d, _, e) = f()

assert (d == 1, "error : d")
print(d)

assert (e == 3, "error : e")
print(e)

Python

The same problem as with Groovy, the underscore works like a real variable :

def f():
    return 1, 2, 3

a, b, c = f()
assert a == 1
print(a)  

assert b == 2
print(b)  

assert c == 3
print(c)

e, _, f = f()

assert e == 1
print(e)

assert _ == 2
print(_)

assert f == 3
print(f)

Kotlin

The same as for Swift, it really works, you cannot reference the underscore :

fun f(): Array<Int> {
    return arrayOf(1,2,3)
}

fun main(args: Array<String>) {
    val (a,b,c) = f()
    assert(a == 1)
    println(a)
    assert(b == 2)
    println(b)
    assert(c == 3)
    println(c)

    val (d, _, e) = f()
    assert(d == 1)
    println(d)
    assert(e == 3)
    println(e)
}