What is Swift Guard Case

What is Guard Case syntax in Swift

The guard-case is a Swift syntax to allow us to precondition check for one specific enum case.

Let's create an enum as an example.

enum Direction {
    case north
    case south
    case east
    case west
}

We can use guard-case to match a single case like this.

let direction = Direction.north

guard case .north = direction else {
    return
}

print("We are heading to north")

Here is the equivalent version of a switch statement.

switch direction {
case .north:
    print("We are heading to north")
case .south, .east, .west:
    break
}

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How to use Guard Case syntax

guard-case has the following syntax.

• The case pattern goes after a guard statement.
• The case pattern followed by the assignment (=) statement.

Here is how it looks.

guard case pattern = enumValue else {}

The case pattern has the same syntax as the switch statement. You can use any pattern that is supported in the switch statement.

Let's see some examples.

Here is an enum with an associated value, Barcode. We will use this in the following examples.

enum Barcode {
    case basic(Int)
    case qrCode(String)
}

Guard case

We can use guard-case to match a single case with the following syntax.

let code = Barcode.qrCode("sarunw")
        
guard case .qrCode = code else {
    return
}
print("QR Code")

Guard case let

And just like a normal switch statement, we can use let to bind an associated value of that enum.

let code = Barcode.qrCode("sarunw")

guard case let .qrCode(content) = code else {
    return
}
print("QR Code: \(content)")