CODEWITHSUNDEEP
swifttype-conversion
al_lea
al_lea

Reputation: 606

How to understand the Int Double conversion in Swift 5.5?

Extend the example in “The Swift Programming Language” (Swift 5.5) “Integer and Floating-Point Conversion”:

3 + 0.14 // allowed

let three = 3
let rest = 0.14

3 + rest // allowed
0.14 + three // compile error
three + 0.14 // compile error

I don’t understand why the last two lines are taken as compile error. Can anyone help to explain a bit? Thanks.

Upvotes: 0

Views: 300

Answers (1)

vadian
vadian

Reputation: 285092

There are two basic rules:

  • A numeric literal without type annotation can be converted implicitly if possible.
  • A constant or variable is initialized with a fixed type which cannot change. A floating point literal becomes Double and an integer literal becomes Int.

So three is Int and 0.14 is Double.

3 + rest works because 3 can be inferred as Double.
But 0.14 cannot be inferred as Int so the last two lines fail to compile.

Upvotes: 3

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