No implicit fallthrough in switch in Swift - Step-by-Step Execution

Concept Flow - No implicit fallthrough in switch

Start switch with value

↓

Match case 1?

No→Match case 2?

↓

Execute case 1

↓

Exit switch

Swift checks each case one by one and runs only the matching case's code without automatically running the next cases.

Execution Sample

Swift

let number = 2
switch number {
case 1:
    print("One")
case 2:
    print("Two")
default:
    print("Other")
}

This code prints the word for the number 2 using a switch statement without running other cases.

Execution Table

Step	Condition Checked	Result	Action	Output
1	number == 1	False	Skip case 1
2	number == 2	True	Execute case 2	Two
3	Exit switch	N/A	Stop checking further cases

💡 Case 2 matched, so switch exits without running other cases.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
number	2	2	2	2

Key Moments - 2 Insights

Why doesn't the switch run the code in case 3 after case 2 matches?

Swift switch statements do not have implicit fallthrough, so after a matching case runs (case 2), the switch exits immediately (see execution_table step 3).

What happens if no case matches the value?

The default case runs if no other case matches, ensuring some code always executes (not shown in this example but explained in concept_flow).

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 2?

A "One"

B "Two"

C "Other"

D No output

💡 Hint

Check the 'Output' column in execution_table row for step 2.

At which step does the switch stop checking cases?

A Step 3

B Step 2

C Step 1

D Never stops

💡 Hint

Look at the 'Action' column in execution_table step 3.

If number was 3, which case would run?

A case 1

B case 2

C default

D No case runs

💡 Hint

Recall the default case runs when no other case matches, as described in concept_flow.

Concept Snapshot

Swift switch checks each case for a match.
Only the matching case runs; no automatic fallthrough.
Use 'default' to catch unmatched values.
No need for break statements.
Switch exits after running matched case.

Full Transcript

This visual trace shows how Swift's switch statement works without implicit fallthrough. The switch checks each case in order. When it finds a matching case, it runs that case's code and then exits immediately without running other cases. For example, when number is 2, case 2 matches, so it prints "Two" and stops. If no case matches, the default case runs. This behavior means you don't need break statements to stop execution like in some other languages.