Extensions vs member functions priority in Kotlin - Visual Side-by-Side Comparison

Concept Flow - Extensions vs member functions priority

Call function on object

↓

Is member function available?

No→Use extension function

Yes↓

Call member function

↓

End

When calling a function on an object, Kotlin first looks for a member function. If none is found, it uses an extension function.

Execution Sample

Kotlin

class Example {
    fun greet() = "Member"
}

fun Example.greet() = "Extension"

fun main() {
    println(Example().greet())
}

This code shows that the member function 'greet' is called instead of the extension function.

Execution Table

Step	Action	Function Found?	Function Called	Output
1	Call greet() on Example instance	Yes, member function	Member function greet()	Member
2	Print output	-	-	Member

💡 Member function exists, so extension function is ignored.

Variable Tracker

Variable	Start	After Call	Final
Example instance	Created	Used to call greet()	No change
Output	None	Member	Member

Key Moments - 2 Insights

Why does the member function get called instead of the extension function?

Because Kotlin always prefers member functions over extension functions when both exist, as shown in execution_table step 1.

What happens if the member function does not exist?

Then Kotlin calls the extension function if available, as the flow shows in the 'No' branch from member function check.

Visual Quiz - 3 Questions

Look at the execution table, what function is called at step 1?

A Extension function greet()

B Member function greet()

C No function is called

D Both member and extension functions

💡 Hint

See execution_table row 1 under 'Function Called'

If the member function greet() was removed, which function would be called?

A Member function greet()

B No function would be called

C Extension function greet()

D Both functions would be called

💡 Hint

Refer to concept_flow where member function absence leads to extension function call

According to variable_tracker, what is the output after calling greet()?

A "Member"

B No output

C "Extension"

D Error

💡 Hint

Check variable_tracker row 'Output' after call

Concept Snapshot

Kotlin calls member functions before extension functions.
If a member function exists, extension with same name is ignored.
Extension functions are used only if no member function matches.
This rule helps avoid ambiguity and keeps member functions priority clear.

Full Transcript

In Kotlin, when you call a function on an object, the language first checks if the object has a member function with that name. If it does, Kotlin calls that member function. If not, Kotlin looks for an extension function with that name and calls it if found. This means member functions have higher priority than extension functions. For example, if a class has a member function greet(), and there is also an extension function greet() for that class, calling greet() on an instance will call the member function. If the member function is removed, then the extension function will be called instead. This priority rule helps keep function calls clear and predictable.