Enum with switch pattern matching in Swift - Step-by-Step Execution

Concept Flow - Enum with switch pattern matching

Define Enum with cases

↓

Create Enum instance

↓

Switch on Enum instance

↓

Match case 1?

No→Match case 2?

↓

Execute case 1

↓

End switch

We define an enum, create an instance, then use a switch to check which case it matches and run code accordingly.

Execution Sample

Swift

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

let dir = Direction.east

switch dir {
case .north:
    print("Going north")
case .south:
    print("Going south")
case .east:
    print("Going east")
case .west:
    print("Going west")
}

This code defines directions, sets one, then prints a message based on the direction using switch.

Execution Table

Step	Action	Enum Instance	Switch Case Checked	Match?	Output
1	Create enum instance	Direction.east	-	-	-
2	Switch start	Direction.east	case .north	No	-
3	Switch continue	Direction.east	case .south	No	-
4	Switch continue	Direction.east	case .east	Yes	Going east
5	Switch ends	Direction.east	-	-	-

💡 Matched case .east, switch ends after executing its block.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
dir	undefined	Direction.east	Direction.east	Direction.east	Direction.east	Direction.east

Key Moments - 3 Insights

Why does the switch check each case one by one?

The switch tries cases in order until it finds a match, as shown in rows 2-4 of the execution table.

What happens if no case matches?

If no case matches, the switch would run a default case if provided, but here it matches at step 4 and stops.

Why do we write cases as .north instead of Direction.north inside switch?

Inside switch on an enum instance, Swift lets us use shorthand .caseName to avoid repetition, as seen in the code sample.

Visual Quiz - 3 Questions

Look at the execution table, what is the enum instance value at step 3?

A Direction.north

B Direction.east

C Direction.south

D Direction.west

💡 Hint

Check the 'Enum Instance' column at step 3 in the execution table.

At which step does the switch find a matching case?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Match?' column to see where it says 'Yes'.

If the enum instance was Direction.west, which case would match?

A case .west

B case .south

C case .north

D case .east

💡 Hint

Refer to the enum cases and how switch matches the instance value.

Concept Snapshot

enum Direction { case north, south, east, west }
let dir = Direction.east
switch dir {
 case .north: ...
 case .south: ...
 case .east: ...
 case .west: ...
}
Use switch to run code based on enum case, matching one case exactly.

Full Transcript

We start by defining an enum called Direction with four cases: north, south, east, and west. Then we create a variable dir and set it to Direction.east. Next, we use a switch statement on dir. The switch checks each case in order: first .north, then .south, then .east. When it reaches .east, it matches and prints 'Going east'. The switch then ends. If no case matched, a default case would run if provided. Inside the switch, we use shorthand .caseName instead of full enum names. This example shows how to use enums with switch pattern matching in Swift.