Lesson 8 of 30 intermediate 4 min read

Structs & methods

Q: When do I use a pointer receiver versus a value receiver?

Use a pointer receiver (`func (r *Receiver)`) when the method needs to modify the struct, or when the struct is large and you want to avoid copying it. Use a value receiver when the method only reads and the struct is small. A common rule of thumb is to be consistent within a type — if any method needs a pointer receiver, use pointer receivers for all of them.

Key takeaways A struct groups related fields into one type; a method is a function attached to a type via a receiver. A pointer receiver (*T) lets a method modify the struct or avoid copying it; a value receiver (T) works on a copy. Go has no classes and no inheritance — structs plus methods, composed together, do the job.

Real programs need to bundle data — a radio channel has a frequency, a bandwidth, a name. This lesson introduces structs to hold that data and methods to give it behaviour.

Defining a struct

type Channel struct {
    Name      string
    FreqHz    float64
    Bandwidth float64
}

Create one and read its fields with dot notation:

cc := Channel{Name: "P25 CC", FreqHz: 851.0125e6, Bandwidth: 12500}
fmt.Println(cc.Name, cc.FreqHz)

Field names starting with a capital letter are exported — visible outside the package. Lowercase fields are private to the package (more in Packages & modules).

Attaching methods

A method is a function with a receiver — the type it belongs to, written before the name:

func (c Channel) Wavelength() float64 {
    return 3e8 / c.FreqHz
}

fmt.Println(cc.Wavelength())

Here c Channel is a value receiver: the method gets a copy of the channel and can only read it.

Pointer vs value receivers

When a method needs to change the struct, it takes a pointer receiver:

func (c *Channel) Retune(freqHz float64) {
    c.FreqHz = freqHz   // modifies the original, not a copy
}

Receiver	Written	Sees	Use when
Value	`func (c Channel)`	a copy	read-only, small structs
Pointer	`func (c *Channel)`	the original	modifying, or large structs

Call it the same way — cc.Retune(852e6) — Go takes the address for you. The rule of thumb: if any method on a type needs a pointer receiver, give them all pointer receivers for consistency.

Composition instead of inheritance

Go has no subclasses. To reuse a struct, you embed it:

type TrunkedChannel struct {
    Channel        // embedded — TrunkedChannel gets Channel's fields and methods
    SystemID int
}

A TrunkedChannel now has Name, FreqHz, and Wavelength() directly, plus its own SystemID. This “has-a” composition is Go’s answer to the “is-a” hierarchies of class-based languages — simpler, and it pairs naturally with the interfaces you’ll meet next.

Quick check: a method needs to change a field of its struct. Which receiver does it need?

Recap

A struct bundles named fields; capitalized fields are exported.
A method attaches behaviour to a type through a receiver.
Pointer receivers modify the original or avoid copying; value receivers work on a copy.
Go uses composition (embedding), not inheritance, to reuse types.

Next up: interfaces — the idea that makes Go code flexible without class hierarchies.

Frequently asked questions

Does Go have classes?

No. Go has structs (bundles of named fields) and methods (functions attached to a type). Together they cover most of what classes do, but there is no inheritance. Instead, Go favours composition — embedding one struct inside another — and interfaces for shared behaviour.

When do I use a pointer receiver versus a value receiver?

Use a pointer receiver (func (r *Receiver)) when the method needs to modify the struct, or when the struct is large and you want to avoid copying it. Use a value receiver when the method only reads and the struct is small. A common rule of thumb is to be consistent within a type — if any method needs a pointer receiver, use pointer receivers for all of them.