If as an expression returning value in Kotlin - Step-by-Step Execution

Concept Flow - If as an expression returning value

Evaluate condition

↓

Condition true?

No→Evaluate else branch

↓

Return else value

↓

Evaluate then branch

↓

Return then value

↓

Use returned value

The if expression evaluates a condition, then returns the value of the 'then' or 'else' branch accordingly.

Execution Sample

Kotlin

val max = if (a > b) a else b
println(max)

This code assigns the greater of a and b to max using if as an expression, then prints max.

Execution Table

Step	Condition (a > b)	Branch Taken	Returned Value	Output
1	5 > 3	then	5
2	N/A	N/A	5	5
3	2 > 4	else	4
4	N/A	N/A	4	4
5	3 > 3	else	3
6	N/A	N/A	3	3

💡 Execution stops after returning value from if expression and printing it.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
a	5	5	2	3	3
b	3	3	4	3	3
max	unassigned	5	4	3	3

Key Moments - 3 Insights

Why does the if expression return a value instead of just running code?

Because in Kotlin, if is an expression that evaluates to the value of the branch taken, as shown in execution_table rows 1 and 3.

What happens if the condition is false and there is no else branch?

The code will not compile because if used as an expression must have an else branch to return a value, as implied by the need to return a value in all cases.

Can the returned value from if be assigned directly to a variable?

Yes, as shown in execution_table where max is assigned the returned value from the if expression.

Visual Quiz - 3 Questions

Look at the execution_table, what is the returned value when a=5 and b=3 at step 1?

A 8

B 5

C 3

D false

💡 Hint

Check the 'Returned Value' column at step 1 where condition is true.

At which step does the condition evaluate to false and the else branch is taken?

A Step 1

B Step 2

C Step 3

D Step 6

💡 Hint

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

If we remove the else branch, what will happen when compiling this code?

A It will cause a compile error

B It will compile and run normally

C It will return null

D It will return zero

💡 Hint

Refer to key_moments about the necessity of else branch for if expressions.

Concept Snapshot

if expression syntax:
val result = if (condition) value1 else value2

- Evaluates condition
- Returns value1 if true
- Returns value2 if false
- Must have else branch when used as expression
- Can assign returned value directly to variable

Full Transcript

In Kotlin, if can be used as an expression that returns a value. The program checks the condition; if true, it evaluates and returns the 'then' branch value; if false, it evaluates and returns the 'else' branch value. This returned value can be assigned directly to a variable. The execution table shows examples with different values of a and b, demonstrating which branch is taken and what value is returned. Remember, when using if as an expression, you must include an else branch to cover all cases. This makes your code concise and expressive.