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.

CodePudding user response：

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.