Swift3中的可选结构

Question

I would like to declare a variable that stores an optional struct like so:

struct my_struct{
    var x: Double
    var y: Double
}

var my_variable = my_struct?

Am I right that this syntax was correct in Swift2? Unfortunately, it is not working in Swift3 anymore. What would be the "new" way to achieve this?

Answer 1

The syntax does not work in Swift 2 either.

First of all let's use a Swift compliant name

struct MyStruct { ... }

You have two options:

• myVariable : MyStruct? declares an optional struct without a value ( nil )

• myVariable : MyStruct? = MyStruct() myVariable : MyStruct? = MyStruct() declares an optional empty struct.

Note: Consider that you have to assign default values for the properties of the struct in the second form or use the memberwise initializer or write a custom initializer.

PS: Don't use optionals as a don't-care alibi. Swift encourages you to use non-optional types a much as possible.

Answer 2

struct my_struct{
    var x: Double
    var y: Double
}

var my_variable:my_struct?

Note that types are usually capitalized and camel-cased by convention in Swift eg

struct MyStruct {
    var x: Double
    var y: Double
}

var myVariable: MyStruct?