If, If Else ExampleUse an if-else statement. Conditions in an if evaluate to true or false.
Swift
If, else. In Swift, we find traditional C-like if-statements. We use "else if" after an if and follow up with an else block—this is standard. Other features. The Swift language supports ternary statements and guard statements. And the "if let" syntax allows us to unwrap a value easily.
Guard
Optional
First example. This program uses an if-statement. It tests the var also with an else-if and an else. The size is 10, so the else-if part matches.
Tip No parentheses are required around the expression being tested in an if-statement.
Tip 2 The else-if and else can be on the same line as the closing brace, or a newline. Either is accepted. var size = 10 // Test size var in if, else-if block. if size >= 20 { print("Big") } else if size >= 10 { print("Medium") } else { print("Small") }
Medium
Ternary. Swift supports a ternary statement. This uses a question mark after an initial condition. If the condition is true, the first value after the question mark is used.
And If the condition is false, the second value is used. Here we assign an Int based on the argument to the test() func.
func test(x: Int) { // Use a ternary statement. // Set y to 5 if x is 10. // ... Set it to 0 otherwise. let y = x == 10 ? 5 : 0 print(y) } // Call ternary test method. test(x: 10) test(x: 200)
5 0
If let, optional binding. A constant can be introduced in an if-statement. Here we use the "if let" construct to look up a value in a dictionary.
Dictionary
Detail If the value exists (is not nil) the inner statements of the if are reached. We can access the constant directly.
However If the dictionary has no data at that key (the value is nil) the inner statements of the if are not reached.
let animals = ["cat": 5, "dog": 2] // Execute inner block if constant is not nil. if let catCount = animals["cat"] { // This gives us a non-nil dictionary value. print(catCount) } if let birdCount = animals["bird"] { // The value is nil, so this is not reached. print(birdCount) } else { print(0) // Reached. }
5 0
Bool, true and false. A bool can store the result of an expression (one that evaluates to true or false). With an if-statement, we can then test the bool. This simplifies some programs.
Here We store the result of the even() method in constant bools. We then test those constants against true and false.
func even(left: Int, right: Int) -> Bool { // Return a bool if the two arguments are equal. return left == right } // Get a bool result. let even1 = even(left: 10, right: 20) if even1 == false { print("Sides not even") } // Use bool type. let even2: Bool = even(left: 40, right: 40) if even2 == true { print("Sides are even") }
Sides not even Sides are even
Guard. This statement is like an if-statement, but it must return or break. It is used to validate arguments. It helps enforce a program's correctness at runtime.
Guard
A summary. Ifs are used in nearly every program. They encode simple condition tests better than switches. But switches allow more complex, detailed branches.
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Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.