Using Enums with Switch/Case Statement in Swift

One of the strengths of using the `switch` statement is pattern matching. Learn all about how to use enums with switch/case statements in Swift in this article!
Written by

Chris C

Last Updated on

Feb 03 2023

Written by Iñaki Narciso

Written for Swift 5.7

One of the strengths of using the switch statement is pattern matching. Say you have a set of values you wanted to check using switch, the compiler will make sure you get to cover an exhaustive list of cases that correspond to all possible values.

This is to make sure that you won’t miss anything, and if you do, the Swift compiler will tell you. This is one of the differences between using switch instead of if.

When you use if, the compiler won’t be strict in reminding you that you need to check for an exhaustive list of values, but rather gives you the flexibility to only check what you need.

So if you have a set of values you want to check for matches, the best conditional statement to use is the switch statement.

For example, you have an Enumeration about all of the planets in the Solar system, and you wanted to perform a switch statement over an enum variable such as follows:

enum Planet {
	case mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
}

let planet: Planet = .earth
switch planet {
case .mercury:
	print("The planet closest to the sun")
case .earth:
	print("This is where we live")
case .neptune:
	print("The planet farthest from the sun of the Solar system")
}

Write the code above, and you’ll get a compiler error Switch must be exhaustive. This is the way the Swift compiler tells you that you need to take into account all possible values.

So what you can do is either click on the error and choose “Add missing cases”, which will then add more switch cases for all remaining values of the Planet enum, or you can choose to ignore the error and add a default case.

Option 1: Adding missing cases

When you choose to “Add missing cases”, the Swift compiler will add all remaining switch cases for you. This would make it easier to complete the exhaustive list of switch cases for you to handle.

switch planet {
case .mercury:
	print("The planet closest to the sun")
case .earth:
	print("This is where we live")
case .neptune:
	print("The planet farthest from the sun of the Solar system")

case .venus:
	addcode
case .mars:
	addcode
case .jupiter:
	addcode
case .saturn:
	addcode
case .uranus:
	addcode
}

Option 2: Adding a default case

You can also add a default case if you choose not to do an exhaustive list of cases.

switch planet {
case .mercury:
	print("The planet closest to the sun")
case .earth:
	print("This is where we live")
case .neptune:
	print("The planet farthest from the sun of the Solar system")
default:
	print("A planet inside the Solar system.")
}

Both options work, but for added safety, I would recommend opting for an exhaustive list of switch cases. This way you also get to use the built-in Swift compiler safety features.

That’s all for now! See you on the next one!

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