Methods

Attach behaviour to types with methods, choose the right receiver, and design clean APIs around your data types.

7 min readProgramming Foundations (Go)Code

Method Syntax

A method is a function with a receiver — an extra parameter that appears before the function name. The receiver binds the function to a type, making it callable with dot notation.

Godefining-and-calling-methods.go

40 linesLn 1, Col 1Go

The receiver `c Circle` makes `Area` a method on `Circle`. Inside the method, `c` is the value of the Circle that `Area()` was called on. The receiver name is usually the first letter of the type — short but consistent.

Value vs Pointer Receivers

A value receiver gets a copy of the value. A pointer receiver gets the address of the value. Use a pointer receiver when the method needs to modify the receiver, or when copying the value would be expensive.

Gopointer-receiver-modifies-the-original.go

40 linesLn 1, Col 1Go

Go automatically takes the address when you call a pointer-receiver method on an addressable value: `c.Increment()` is shorthand for `(&c).Increment()`. This convenience disappears when the value is not addressable (e.g. returned from a function and not stored).

Receiver type	Can mutate?	Use when
Value `(c T)`	No — gets a copy	Read-only; small, cheap-to-copy type
Pointer `(c *T)`	Yes — gets the address	Mutation needed; large struct; type has a mutex

Be consistent within a type

If any method on a type needs a pointer receiver, make all methods use pointer receivers. Mixing value and pointer receivers on the same type is confusing and causes surprising interface-satisfaction behaviour.

Method Sets

The method set of a type is the complete list of methods you can call on it. A *T value can call all methods defined with *T and T receivers. A plain T value can only call methods with T receivers.

Gomethod-sets-and-addressability.go

20 linesLn 1, Col 1Go

Local variables are addressable, so Go auto-dereferences when calling pointer-receiver methods on them. Function return values are not addressable — you must store the value first before calling pointer-receiver methods.

Methods on Non-Struct Types

You can define methods on any named type defined in your package, not just structs. This is commonly used to add display, conversion, or validation behaviour to primitive-based types.

Gomethods-on-a-named-string-type.go

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`Direction` is just a named `string`, but we can attach methods to it. Implementing `String() string` makes `fmt` use it for printing automatically — this is the `fmt.Stringer` interface, which you will learn about next.

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Stage 1 · Code

Methods, Interfaces & Errors

Methods

Attach behaviour to types with methods, choose the right receiver, and design clean APIs around your data types.

7 min readProgramming Foundations (Go)Code

Method Syntax

A method is a function with a receiver — an extra parameter that appears before the function name. The receiver binds the function to a type, making it callable with dot notation.

Godefining-and-calling-methods.go

40 linesLn 1, Col 1Go

Value vs Pointer Receivers

Gopointer-receiver-modifies-the-original.go

40 linesLn 1, Col 1Go

Receiver type	Can mutate?	Use when
Value `(c T)`	No — gets a copy	Read-only; small, cheap-to-copy type
Pointer `(c *T)`	Yes — gets the address	Mutation needed; large struct; type has a mutex

Be consistent within a type

Method Sets

Gomethod-sets-and-addressability.go

20 linesLn 1, Col 1Go

Methods on Non-Struct Types

You can define methods on any named type defined in your package, not just structs. This is commonly used to add display, conversion, or validation behaviour to primitive-based types.

Gomethods-on-a-named-string-type.go

40 linesLn 1, Col 1Go

Mark this lesson complete to store local progress and unlock a cleaner resume path the next time you visit.