This vs it receiver difference in Kotlin - Visual Side-by-Side Comparison

Concept Flow - This vs it receiver difference

Start function with receiver

↓

Use 'this' to refer to receiver object

↓

Use 'it' in lambda for implicit parameter

↓

Perform actions using 'this' or 'it'

↓

Return or end function

Shows how 'this' refers to the receiver object in extension functions, while 'it' is the implicit name for lambda parameters.

Execution Sample

Kotlin

fun String.showThis() {
    println(this)       // 'this' is the String receiver
    listOf(1, 2).forEach {
        println(it)     // 'it' is each element in the list
    }
}

Prints the receiver string using 'this' and each list element using 'it' inside a lambda.

Execution Table

Step	Code Line	Receiver/Object	'this' Value	'it' Value	Output
1	fun String.showThis() {	String receiver	String receiver	N/A	No output
2	println(this)	String receiver	String receiver	N/A	Hello
3	listOf(1, 2).forEach {	List<Int>	String receiver	1	No output
4	println(it)	List<Int>	String receiver	1	1
5	forEach next iteration	List<Int>	String receiver	2	No output
6	println(it)	List<Int>	String receiver	2	2
7	End of function	String receiver	String receiver	N/A	No output

💡 Function ends after printing receiver string and all list elements.

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 6	Final
this (receiver)	N/A	"Hello"	"Hello"	"Hello"	"Hello"
it (lambda param)	N/A	N/A	1	2	N/A

Key Moments - 2 Insights

Why does 'this' refer to the string but 'it' refers to list elements?

'this' refers to the receiver object of the extension function (the string), while 'it' is the implicit name for each element inside the lambda passed to forEach (the list elements). See execution_table rows 2 and 4.

Can 'this' be used inside the lambda instead of 'it'?

No, inside the lambda 'this' still refers to the outer receiver (the string), not the lambda parameter. 'it' is used for the lambda's current element. See execution_table rows 4 and 6.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'this' at step 4?

A 2

B 1

C "Hello"

D N/A

💡 Hint

Check the 'this' Value column at step 4 in execution_table.

At which step does 'it' first get the value 2?

A Step 6

B Step 3

C Step 5

D Step 4

💡 Hint

Look at the 'it' Value column in execution_table rows 4 and 6.

If we replaced 'println(it)' with 'println(this)' inside the lambda, what would print?

A Each list element (1, then 2)

B The receiver string each time

C Nothing

D Compilation error

💡 Hint

Refer to key_moments about 'this' inside lambda and execution_table rows 4 and 6.

Concept Snapshot

In Kotlin extension functions, 'this' refers to the receiver object.
Inside lambdas, 'it' is the implicit name for the single parameter.
'this' inside a lambda still points to the outer receiver.
Use 'it' to access lambda elements.
This distinction helps avoid confusion when nesting lambdas.

Full Transcript

This visual shows how 'this' and 'it' work differently in Kotlin. 'this' refers to the receiver object of an extension function, like a string. When you use a lambda, like in forEach, 'it' is the implicit name for each element in the list. The execution table traces each step: first printing the receiver string with 'this', then printing each list element with 'it'. The variable tracker shows 'this' stays the same, while 'it' changes per element. Key moments explain why 'this' and 'it' are different and why you can't use 'this' to mean the lambda parameter. The quiz tests understanding by asking about values of 'this' and 'it' at different steps and what happens if you swap them. Remember, 'this' is the receiver, 'it' is the lambda parameter.