Iterating enum cases with CaseIterable in Swift - Step-by-Step Execution

Concept Flow - Iterating enum cases with CaseIterable

Define enum with CaseIterable

↓

Access allCases property

↓

Start loop over allCases

↓

Process each enum case

↓

Loop ends when all cases processed

This flow shows how to define an enum with CaseIterable, then loop through all its cases using the allCases property.

Execution Sample

Swift

enum Direction: CaseIterable {
    case north, south, east, west
}

for dir in Direction.allCases {
    print(dir)
}

This code defines an enum Direction with four cases and prints each case by iterating over allCases.

Execution Table

Iteration	dir (enum case)	Action	Output
1	north	Print dir	north
2	south	Print dir	south
3	east	Print dir	east
4	west	Print dir	west
-	-	Loop ends	All cases printed

💡 All enum cases have been iterated, loop ends.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
dir	-	north	south	east	west	-

Key Moments - 3 Insights

Why can we use Direction.allCases in the for loop?

Because the enum Direction conforms to CaseIterable, Swift automatically provides the allCases collection of all enum cases, as shown in the execution_table rows 1 to 4.

What happens if we add a new case to the enum?

The allCases collection automatically includes the new case, so the loop will iterate over it without any code change, as the execution_table would have an extra iteration.

Can we use allCases with enums that don't conform to CaseIterable?

No, only enums that conform to CaseIterable have the allCases property. Without it, the code would not compile, so the loop cannot run.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of dir at iteration 3?

A east

B south

C north

D west

💡 Hint

Check the 'dir (enum case)' column at iteration 3 in the execution_table.

At which iteration does the loop end according to the execution_table?

A After iteration 3

B After iteration 5

C After iteration 4

D It never ends

💡 Hint

Look at the exit_note and the last row of the execution_table.

If we add a new case 'up' to the enum, how would the execution_table change?

A The loop would skip the new case

B It would have one more iteration with dir = up

C The code would not compile

D The output would be empty

💡 Hint

Refer to key_moments about adding new cases and how allCases updates automatically.

Concept Snapshot

enum MyEnum: CaseIterable {
    case a, b, c
}

for item in MyEnum.allCases {
    // use item
}

- CaseIterable auto-creates allCases array
- Looping over allCases visits every enum case
- Adding cases updates allCases automatically

Full Transcript

This example shows how to use the CaseIterable protocol in Swift to loop over all cases of an enum. First, we define an enum Direction with cases north, south, east, and west, and make it conform to CaseIterable. This gives us access to Direction.allCases, a collection of all enum cases. Then, we use a for loop to go through each case in allCases and print it. The execution_table shows each iteration with the current enum case and the printed output. The variable_tracker shows how the variable dir changes each iteration. Key moments clarify why allCases works only with CaseIterable enums and how adding new cases affects the loop. The visual quiz tests understanding of the iteration steps and behavior when modifying the enum. The concept snapshot summarizes the syntax and behavior for quick reference.