Structs

We use structs in Go to represent structured data. It's often convenient to group different types of variables together. For example, if we want to represent a car we could do the following:

type car struct {
	brand      string
	model      string
	doors      int
	mileage    int
}

This creates a new struct type called car. All cars have a brand, model, doors and mileage.

Structs in Go are often used to represent data that you might use a dictionary or object for in other languages.

1

Creating (instantiating) a struct

You can make a new car value in a few different ways:

Option 1: Using field names (recommended)

myCar := car{
	brand:   "Toyota",
	model:   "Corolla",
	doors:   4,
	mileage: 25000,
}

• This creates a new car struct.

• The variable myCar now holds all that data together.

2

Option 2: Without field names (less common)

myCar := car{"Honda", "Civic", 2, 15000}

This works too, but you must follow the exact order the fields were defined in the struct (brand, model, doors, mileage).

If the struct changes later (like you add a new field), this version can break — that’s why named fields are safer.

3

Option 3: Create an empty struct and fill it later

var myCar car
myCar.brand = "Ford"
myCar.model = "Focus"
myCar.doors = 4
myCar.mileage = 32000

This works if you want to create an empty car and fill it step-by-step.

---

Accessing struct fields

Once you’ve created it, you can access its fields using the dot (.) operator:

fmt.Println(myCar.brand)   // Toyota
fmt.Println(myCar.mileage) // 25000

You can also modify them:

myCar.mileage += 1000
fmt.Println(myCar.mileage) // 26000

---

1

Example: Using it in a function

func printCarInfo(c car) {
	fmt.Printf("This %v %v has %v doors and %v miles.\n",
		c.brand, c.model, c.doors, c.mileage)
}

func main() {
	myCar := car{
		brand:   "Toyota",
		model:   "Corolla",
		doors:   4,
		mileage: 25000,
	}
	printCarInfo(myCar)
}

Output:

This Toyota Corolla has 4 doors and 25000 miles.

---

TL;DR — Summary

Action	Example	Description
Define struct	type car struct {...}	Defines a new type
Create (instantiate)	myCar := car{brand: "Toyota", ...}	Creates a struct value
Access field	myCar.brand	Reads or writes a field
Pass to function	printCarInfo(myCar)	Structs can be passed by value
Modify field	myCar.mileage += 1000	Updates data inside struct

Calling a Struct in a Function

type car struct { brand string model string doors int mileage int }

1

Create a function that accepts a struct as a parameter

When you want to use your struct inside a function, you pass it in like any other variable — you just give it the type of the struct (car in this case).

func printCarInfo(c car) {
	fmt.Printf("Brand: %s\nModel: %s\nDoors: %d\nMileage: %d\n",
		c.brand, c.model, c.doors, c.mileage)
}

• The parameter c is of type car.

• Inside the function, you can access all of its fields with c.fieldName.

2

Create a car in main and call the function

func main() {
	myCar := car{
		brand:   "Toyota",
		model:   "Corolla",
		doors:   4,
		mileage: 25000,
	}
	printCarInfo(myCar)
}

Output:

Brand: Toyota
Model: Corolla
Doors: 4
Mileage: 25000

3

Passing by value vs pointer (optional but important)

By default, Go passes structs by value — meaning it sends a copy to the function. If you modify the struct inside the function, it won’t affect the original one unless you pass it by pointer.

Example — by value (copy):

func resetMileage(c car) { c.mileage = 0 }

func main() {
	myCar := car{"Honda", "Civic", 2, 10000}
	resetMileage(myCar)
	fmt.Println(myCar.mileage) // still 10000 (unchanged)
}

Example — by pointer (reference):

func resetMileage(c *car) { c.mileage = 0 }

func main() {
	myCar := car{"Honda", "Civic", 2, 10000}
	resetMileage(&myCar) // pass the address
	fmt.Println(myCar.mileage) // now 0
}

4

Adding a method (bonus)

You can also attach a function directly to a struct type — this is called a method.

func (c *car) drive(miles int) {
	c.mileage += miles
	fmt.Printf("Drove %d miles, new mileage: %d\n", miles, c.mileage)
}

func main() {
	myCar := car{"Ford", "Focus", 4, 32000}
	myCar.drive(150)
}

Output:

Drove 150 miles, new mileage: 32150

---

TL;DR Summary

Concept	Example	Description
Pass struct to function	printCarInfo(myCar)	Sends a copy of the struct
Access inside function	c.brand, c.mileage	Use the dot (.) operator
Modify struct in function	func update(c *car)	Pass a pointer (*car) to change it
Method on struct	func (c *car) drive()	Attaches function directly to struct type