Why operators are functions in Kotlin - Visual Breakdown

Concept Flow - Why operators are functions in Kotlin

Start with expression

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Operator seen: +

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Translate + to function call

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Call function plus() on object

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Function executes and returns result

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Use returned result in expression

Kotlin treats operators like + as calls to functions, so using an operator is just calling a function behind the scenes.

Execution Sample

Kotlin

val a = 5
val b = 3
val c = a + b // calls a.plus(b)

This code adds two numbers using +, which Kotlin turns into a function call plus() on a.

Execution Table

Step	Code Line	Action	Function Called	Result
1	val a = 5	Assign 5 to a	None	a = 5
2	val b = 3	Assign 3 to b	None	b = 3
3	val c = a + b	Detect + operator	plus	Call a.plus(b)
4	val c = a + b	plus function adds values	plus	Returns 8
5	val c = a + b	Assign result to c	None	c = 8

💡 Expression evaluated, c holds the sum 8

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 5
a	undefined	5	5	5
b	undefined	undefined	3	3
c	undefined	undefined	undefined	8

Key Moments - 2 Insights

Why does Kotlin treat + like a function call?

Because operators are just special function calls like plus(), Kotlin can let you define how + works for your own types. See step 3 and 4 in execution_table.

Is + a special keyword or a function in Kotlin?

It looks like a symbol but Kotlin converts it to a function call internally, so + is actually calling plus() on the object. See execution_table step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what function is called when using the + operator?

A sum

B plus

C add

D operatorPlus

💡 Hint

Check the 'Function Called' column at step 3 and 4 in execution_table.

At which step is the result of a.plus(b) assigned to variable c?

A Step 3

B Step 4

C Step 5

D Step 2

💡 Hint

Look at the 'Action' column describing assignment to c in execution_table.

If we replaced + with a custom operator, what would Kotlin do?

A Call a different function matching that operator

B Throw a syntax error

C Ignore the operator and do nothing

D Automatically convert it to plus()

💡 Hint

Kotlin maps operators to functions, so a new operator means calling a matching function (see concept_flow).

Concept Snapshot

In Kotlin, operators like + are actually function calls.
Using a + b calls a.plus(b) behind the scenes.
This lets you define how operators work for your own types.
Operators are just special syntax for functions.
This design makes Kotlin flexible and consistent.

Full Transcript

Kotlin treats operators such as + as function calls. When you write a + b, Kotlin translates it to a call to the function plus() on the object a with b as argument. This means operators are not special keywords but functions with special syntax. This allows Kotlin to let you define how operators behave for your own classes by defining functions like plus(). The execution steps show assigning values to variables a and b, then calling plus() when + is used, and finally assigning the result to c. This approach makes Kotlin flexible and consistent in handling operations.