guard 문

Early Exit

A guard statement, like an if statement, executes statements depending on the Boolean value of an expression. You use a guard statement to require that a condition must be true in order for the code after the guard statement to be executed. Unlike an if statement, a guard statement always has an else clause—the code inside the else clause is executed if the condition is not true.

func greet(person: [String: String]) {
    guard let name = person["name"] else {
        return    
}        print("Hello \(name)!")        
guard let location = person["location"] else {
        print("I hope the weather is nice near you.")
        return    
}        
print("I hope the weather is nice in \(location).")
}
greet(["name": "John"])
// Prints "Hello John!"
// Prints "I hope the weather is nice near you."
greet(["name": "Jane", "location": "Cupertino"])
// Prints "Hello Jane!"
// Prints "I hope the weather is nice in Cupertino."

 

If the guard statement’s condition is met, code execution continues after the guard statement’s closing brace. Any variables or constants that were assigned values using an optional binding as part of the condition are available for the rest of the code block that the guard statement appears in.

If that condition is not met, the code inside the else branch is executed. That branch must transfer control to exit the code block in which the guard statement appears. It can do this with a control transfer statement such as return, break, continue, or throw, or it can call a function or method that doesn’t return, such as fatalError().