Statement guard
- used inside an if statement, a loop, or a function
- code in the
else clause runs if the condition is false - requires a true condition in order for code to run (like a positive if stmt)
- optional variables are unwrapped in the scope of the guard
- must exit via:
return – function, continue break – if stmt or loop
Guard in Loop
// in a loop -> 1, 2, 3, -4 isn't positive, 5
let positiveArray = [1, 2, 3, -4, 5]
for pos in positiveArray {
guard pos >= 0 else {
print("\(pos) isn't positive")
continue
}
print("\(pos)")
}
- use
break to completely leave the loop
Guard in Function
func greet(person: String?) {
guard let personName = person else {
print ("Hey no name")
return
}
print("Hello \(personName)")
}
// -> Hello John
greet(person: "John")
// -> Hey no name
greet(person: nil)
Early Exit in Guard Function
func greetLastName(name: (first: String, last: String?)) -> Int {
guard name.last != nil else {
print("Last name required")
return 0
}
return 1
}
// -> Last name required, exit with return 0
greetLastName(name: ("Matt", nil))
Guard stops the Pyramid of Doom
- POD -> nexted if statements
func sendToServer(name: String, address: String) {
print("sending stuff")
}
func guardSubmit() {
guard let name = nameField.text else {
print("No name to submit")
return
}
guard let address = addressField.text else {
print("No address to submit")
return
}
sendToServer(name: name, address: address)
}
Pyramid of Doom -> example to avoid
func nonguardSubmit() {
// pyramid of doom starts here
if let name = nameField.text {
if let address = addressField.text {
sendToServer(name: name, address: address)
} else {
print("no address to submit")
}
} else {
print("no name to submit")
}
}
