Why does swift conversion work for floating point division?

Question

Like in many languages, Swift's division operator defaults to integer division, so:

let n = 1 / 2
print(n) // 0

If you want floating point division, you have to do

let n1 = 1.0 / 2
let n2 = 1 / 2.0
let n3 = Double(1) / 2
let n4 = 1 / Double(2)

print(n1) // 0.5
print(n2) // 0.5
print(n3) // 0.5
print(n4) // 0.5

Again, like most other languages, you can't cast the whole operation:

let n5 = Double(1 / 2)
print(n5) // 0.0

Which happens because swift performs the integer division of 1 and 2 (1 / 2) and gets 0, which it then tries to cast to a Double, effectively giving you 0.0.

I am curious as to why the following works:

let n6 = (1 / 2) as Double
print(n6) // 0.5

I feel like this should produce the same results as Double(1 / 2). Why doesn't it?

Answer 1

1 and 2 are literals. They have no type unless you give them a type from context.

let n6 = (1 / 2) as Double

is essentially the same as

let n6: Double = 1 / 2

that means, you tell the compiler that the result is a Double. That means the compiler searches for operator / with a Double result, and that means it will find the operator / on two Double operands and therefore considers both literals as of type Double.

On the other hand,

let n5 = Double(1 / 2)

is a cast (or better said, initialization of a Double). That means the expression 1 / 2 gets evaluated first and then converted to Double.