Swift Tour Summary (3), swifttour

Swift Tour Summary (3), swifttour

About Optional Control Flow

If let constantName = someOptional {

Statements

}

If the Optional is nil, if is not entered; otherwise, the execution and constantName are the value of the Optional.

Example:

If let actualNumber = possibleNumber. toInt (){

Println ("\ (possibleNumber) has an integer value of \ (actualNumber )")

} Else {

Println ("\ (possibleNumber) cocould not be converted to an integer ")

}

// Prints "123 has an integer value of 123"

About nil

Optional can be assigned a value of nil.

For example:

Var serverResponseCode: Int? = 404

ServerResponseCode = nil

 

Var surveyAnswer: String?

// SurveyAnswer is automatically set to nil

 

Expansion of optional: Implicitly Unwrapped Optionals

Sometimes, an optional will be safe after the first assignment, and nil check is not required.

Definition: String! Instead of String?

Example:

Let possibleString: String? = "An optional string ."

Println (possibleString !) // Requires an exclamation mark to access this value

// Prints "An optional string ."

 

Let assumedString: String! = "An implicitly unwrapped optional string ."

Println (assumedString) // no exclamation mark is needed to access its value

// Prints "An implicitly unwrapped optional string ."

 

For this special type (IUO), general optional usage is applicable:

If assumedString {

Println (assumedString)

}

 

Assertions-debugging

Let age =-3

Assert (age> = 0, "A person's age cannot be less than zero ")

// Assertion trigger