Nested structs in Go - Step-by-Step Execution

Concept Flow - Nested structs

Define Outer Struct

↓

Define Inner Struct

↓

Create Outer Struct Instance

↓

Assign Inner Struct to Outer

↓

Access Inner Struct Fields

↓

Use Nested Data

This flow shows how to define a struct inside another struct, create instances, assign values, and access nested fields.

Execution Sample

Go

package main

import "fmt"

type Address struct {
    City string
    Zip  int
}

type Person struct {
    Name    string
    Address Address
}

func main() {
    p := Person{Name: "Alice", Address: Address{City: "NYC", Zip: 10001}}
    fmt.Println(p.Name, p.Address.City, p.Address.Zip)
}

This code defines two structs, Person and Address, nests Address inside Person, creates a Person instance, and prints nested fields.

Execution Table

Step	Action	Variable/Field	Value	Notes
1	Define struct Address	Address	struct with City(string), Zip(int)	Struct type created
2	Define struct Person	Person	struct with Name(string), Address(Address)	Struct type created with nested struct
3	Create Person instance p	p.Name	"Alice"	Name field set
3	Create Person instance p	p.Address.City	"NYC"	Nested City field set
3	Create Person instance p	p.Address.Zip	10001	Nested Zip field set
4	Print p.Name	Output	"Alice"	Access outer struct field
4	Print p.Address.City	Output	"NYC"	Access nested struct field
4	Print p.Address.Zip	Output	10001	Access nested struct field
5	End of main	-	-	Program ends

💡 Program ends after printing nested struct fields

Variable Tracker

Variable	Start	After Step 3	Final
p.Name	""	"Alice"	"Alice"
p.Address.City	""	"NYC"	"NYC"
p.Address.Zip	0	10001	10001

Key Moments - 2 Insights

Why do we write p.Address.City instead of just p.City?

Because City is inside the nested Address struct, so we must access it through p.Address as shown in execution_table rows 4-7.

Can we assign Address fields directly without creating Address struct first?

No, we must create the Address struct instance first and assign it to p.Address, as shown in step 3 of execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of p.Address.Zip after step 3?

A 10001

B 0

C "NYC"

D "Alice"

💡 Hint

Check execution_table row 5 where p.Address.Zip is set to 10001

At which step do we assign the Name field of p?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at execution_table row 3 where p.Name is set to "Alice"

If we tried to print p.City directly, what would happen?

A It prints the city name

B It prints empty string

C Compilation error: p.City undefined

D It prints zero

💡 Hint

Refer to key_moments question 1 about accessing nested fields

Concept Snapshot

Nested structs in Go:
- Define inner struct type
- Use inner struct as field in outer struct
- Create outer struct instance with inner struct values
- Access nested fields with dot notation (outer.inner.field)
- Nested structs group related data clearly

Full Transcript

This example shows how to use nested structs in Go. First, we define an Address struct with City and Zip fields. Then, we define a Person struct that includes a Name and an Address field. We create a Person instance named p, setting Name to "Alice" and Address to an Address instance with City "NYC" and Zip 10001. We print p.Name, p.Address.City, and p.Address.Zip. The execution table traces each step, showing how fields are assigned and accessed. Key points include accessing nested fields with p.Address.City and the need to create the nested struct instance before assigning it. The quiz checks understanding of these steps. This helps organize complex data clearly in Go programs.