Menu
Default values can be assigned to a struct by using a constructor function. Rather than creating a structure directly, we can use a constructor to assign custom default values to all or some of its members. Another way of assigning default values to structs is by using tags.
When we define a struct (or class) type, we can provide a default initialization value for each member as part of the type definition. This process is called non-static member initialization, and the initialization value is called a default member initializer.
// In C++ We can Initialize the Variables with Declaration in Structure. Structure members can be initialized using curly braces '{}'. For example, following is a valid initialization.
If a structure variable does not have an initializer, the initial values of the structure members depend on the storage class associated with the structure variable: If a structure variable has static storage, its members are implicitly initialized to zero of the appropriate type.
Swift 5.1:
Variables, marked with var are optional in constructors and their default value will be used. Example:
struct Struct {
var param1: Int = 0
let param2: Bool
}
let s1 = Struct(param2: false) // param1 = 0, param2 = false
let s2 = Struct(param1: 1, param2: true) // param1 = 1, param2 = true
For older versions of Swift (< 5.1):
Default Initialization is all-or nothing for a Struct. Either you define defaults for all properties and you get an automatically generated initializer Struct1() plus an initializer with all of the properties, or you get only the initializer with all of the properties, including any that happen to have a set default value. You're going to have to implement a custom initializer.
struct Struct1 {
let myLet = "my let"
let myLet2: Bool
let myLet3: String
init(myLet2: Bool, myLet3: String) {
self.myLet2 = myLet2
self.myLet3 = myLet3
}
}
Swift 5.1: The struct memberwise initialisation behaviour is changing in Swift 5.1 (which ships with Xcode 11) to behave more as you'd expect:
struct Struct1 {
var myVar = "my var"
let myLet2: Bool
let myLet3: String
}
// Swift 5.1 generates a memberwise init as:
// init(myVar: String = "my var", myLet2: Bool, myLet3: String)
so the following code will now work in Swift 5.1:
let s1 = Struct1(myLet2: false, myLet3: "My url123")
let s2 = Struct1(myVar: "var1", myLet2: false, myLet3: "My url123")
For more details see the relevant Swift evolution proposal
In swift 4
struct Struct1 {
let myLet: String?
let myLet2: Bool
let myLet3: String
init(myLet: String? = nil, myLet2: Bool, myLet3: String) {
self.myLet = myLet
self.myLet2 = myLet2
self.myLet3 = myLet3
}
}
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With