How Can I Declare a Closure in Swift?

Closures is one type of Self-Contained blocks functionality in which passed value and use that in you code. In objective-c known as Blocks that similar Closures in Swift.

This tutorial provide the declaration of the Closures and how can use the Closure in swift.

Declare Closure as Constant : You can declare constant using Closure.

let myFirstClosure = {
    "Kirit Modi"
}

calling the closure and get the value of constant.

myFirstClosure()

Declare Closure as Variable : Passing the string value as closure parameter and get the string value. it means you can get variant value from closure.

var closureName = { (myString : String) -> (String) in
    return myString
}

calling the closure to pass string like "Kirit Modi" and get the variable value also same as passing value.

let myClosure = self.closureName("Kirit Modi")
print(myClosure)

Declare  Closure as parameter with function : 
Define closure syntax type with typealias. 

typealias closure = (Int , Int) -> ()

Declare function with use of closure syntax.

func myClosureFunction(action: closure) -> () {
    action(2,5)
}

calling the closure and get its value inside the function. Here you can get value of A and B inside the block.

self.myClosureFunction { (A, B) in
     print(A)
     print(B)
}

Declare  Closure function with Return type : Define a function name personalDetails with Closure type (( String , String) -> String).  and return another function inside the Closure that return the value of String. See and understand the full code.

func personalDetails () -> ((String, String) -> String) {

    func fullname(name: String, last: String) -> (String) {
        return name + last
    }
    return fullname
}

Calling the above function to make one object of personalDetails.

let details = personalDetails()
print(details("Kirit", "Modi"))

 Thanks.