Swift对类型注释的定义

Question

In Swift Programming Language guide, it has this definition for Type Annotation: "A type annotation explicitly specifies the type of a variable or expression ."

We all know how to specify the type of a variable , but how exactly do you specify the type of an expression ?

Answer 1

The Apple documentation says: "in

let someTuple: (Double, Double) = (2.14159, 2.71828)

the expression someTuple is specified to have the tuple type..." (emphasis mine). Thus a let or var binding is an example using a type annotation on an expression .

A type annotation for a variable is illustrated as specifying the type for a function parameter:

func someFunction(a:Int) { /* ... */ }

Answer 2

You use a colon to tell the compiler what type your expression or variable has.

eg

let year : Int = 2005 let isRaining : Bool = true

The : Int part is the type annotation here.