When with ranges and types in Kotlin - Step-by-Step Execution

Concept Flow - When with ranges and types

Start

↓

Evaluate expression

↓

Check when branches in order

↓

Is value in range?

Yes→Execute branch

↓

Is value of type?

Yes→Execute branch

↓

Else branch

→Execute branch

The 'when' expression evaluates a value, then checks each branch in order to find a matching range or type, executes that branch, and stops.

Execution Sample

Kotlin

val x: Any = 42
when (x) {
  in 1..50 -> println("In range 1 to 50")
  is String -> println("It's a String")
  else -> println("Unknown")
}

Checks if x is in the range 1 to 50, or if x is a String, then prints a message accordingly.

Execution Table

Step	Expression Value	Condition Checked	Condition Result	Branch Taken	Output
1	42	in 1..50	True	in 1..50 branch	In range 1 to 50
2	42	is String	Skipped	No	No output
3	42	else	Skipped	No	No output
4	-	End of when	-	-	-

💡 First condition 'in 1..50' is true, branch executed, when ends.

Variable Tracker

Variable	Start	After Step 1	After Step 4
x	42	42	42

Key Moments - 2 Insights

Why does the 'is String' branch not run even though it's after the range check?

Because the first condition 'in 1..50' is true at step 1, the when expression stops checking further branches as shown in the execution_table rows 1-4.

What happens if the value is not in any range or type checked?

The 'else' branch runs as a fallback, shown in the execution_table row 3, but here it is skipped because a previous branch matched.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output at step 1?

A "Unknown"

B "It's a String"

C "In range 1 to 50"

D No output

💡 Hint

Check the 'Output' column in execution_table row 1.

At which step does the when expression stop checking further branches?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Branch Taken' and 'Condition Result' columns in execution_table rows.

If x was "Hello" instead of 42, which branch would be taken?

A in 1..50 branch

B is String branch

C else branch

D No branch

💡 Hint

Refer to the 'Condition Checked' column and think about type checking.

Concept Snapshot

when (value) {
  in range -> action  // checks if value is in range
  is Type -> action   // checks if value is of a type
  else -> action      // fallback if no match
}
Stops at first matching branch.

Full Transcript

This example shows how Kotlin's when expression works with ranges and types. It evaluates the expression, then checks each branch in order. If the value is in the specified range, it runs that branch and stops. If not, it checks if the value is of a certain type. If none match, it runs the else branch. Here, the value 42 is in the range 1 to 50, so the first branch runs and the others are skipped.