Pointer receivers in Go - Step-by-Step Execution

Concept Flow - Pointer receivers

Define struct

↓

Define method with pointer receiver

↓

Create struct instance

↓

Call method on instance

↓

Method receives pointer

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Modify struct fields

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Changes visible outside method

This flow shows how a method with a pointer receiver modifies the original struct instance by receiving its memory address.

Execution Sample

Go

package main
import "fmt"
type Counter struct { count int }
func (c *Counter) Increment() { c.count++ }
func main() {
 c := Counter{}
 c.Increment()
 fmt.Println(c.count)
}

This code defines a struct with a pointer receiver method that increments a field, showing the change persists after the method call.

Execution Table

Step	Action	Receiver (c)	Field c.count	Output
1	Create Counter instance c	Counter{count:0}	0
2	Call c.Increment()	&c (pointer to c)	0 before increment
3	Inside Increment(), c.count++	&c	1 after increment
4	Return from Increment()	&c	1
5	Print c.count	Counter{count:1}	1	1

💡 Method call finished, c.count is updated to 1 and printed

Variable Tracker

Variable	Start	After Increment call	Final
c.count	0	1	1

Key Moments - 2 Insights

Why does c.count change after calling Increment()?

Because Increment() uses a pointer receiver, it modifies the original struct's field directly, as shown in step 3 and 4 of the execution_table.

What if Increment() used a value receiver instead of a pointer?

Then Increment() would work on a copy of c, so changes to c.count inside the method would not affect the original, unlike the pointer receiver case in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of c.count immediately after step 3?

A 0

B 1

C Undefined

D 2

💡 Hint

Check the 'Field c.count' column at step 3 in the execution_table.

At which step does the method receive a pointer to the struct?

A Step 1

B Step 4

C Step 2

D Step 5

💡 Hint

Look at the 'Receiver (c)' column to see when &c is passed.

If Increment() used a value receiver, what would be the output at step 5?

A 0

B 1

C Compilation error

D Undefined

💡 Hint

Recall that value receivers work on copies, so original c.count remains unchanged.

Concept Snapshot

Pointer receivers in Go methods:
- Use *Type to define pointer receiver
- Method receives address, can modify original struct
- Changes inside method affect caller's instance
- Use pointer receivers to avoid copying large structs
- Enables modifying struct fields directly

Full Transcript

This example shows a Go struct Counter with a method Increment that uses a pointer receiver. When main creates an instance c and calls c.Increment(), the method receives a pointer to c, allowing it to increase the count field directly. The execution table traces each step: creation of c with count 0, calling Increment which receives &c, incrementing count to 1, returning, and finally printing the updated count 1. Key points include that pointer receivers allow methods to modify the original struct, unlike value receivers which work on copies. The visual quiz tests understanding of when the pointer is received, the value changes, and the effect of using value receivers. This helps beginners see how pointer receivers enable methods to change struct data in Go.