Methods can be declared on both pointers and values. The difference is subtle but important.

type Person struct {
     age int
}

// Method's receiver is the value, `Person`.
func (p Person) Age() int {
     return p.age
}

// Method's receiver is a pointer, `*Person`.
func (p *Person) SetAge(age int) {
     p.age = age
}

In reality, you’d only define getter and setter functions like this if you needed to implement additional logic. In an example like this you’d just make the Age field public.

This is how you define getter and setter functions in Go. Notice that we defined the Age() function on the value but SetAge() on the pointer (i.e. *Person). This is important.

Go always passes by value. Function parameters are always passed by copying them as opposed to passing a reference. (Read more.)

Even pointers are technically passed by value. The memory address is copied, the value it points to is not copied.

Here is the wrong way to define SetAge. Let’s see what happens.

func (p Person) SetAge(age int) {
     p.age = age
}

p := Person{}
p.SetAge(10)
fmt.Printf("Age: %v", p.Age()) // Age: 0

▶ Run it.

Notice that the output is 0 instead of 10? This is ‘pass by value’ in action.

Calling p.SetAge(10) passes a copy of p to the SetAge function. SetAge sets the age property on the copy of p that it received which is discarded after the function returns.

Now let’s do it the right way.

func (p *Person) SetAge(age int) {
     p.age = age
}

p := Person{}
p.SetAge(10)
fmt.Printf("Age: %v", p.Age()) // Age: 10

▶ Run it.

My rule of thumb is this: declare the method on the pointer unless your struct is such that you don’t use pointers to it.

Two reasons:

1. Performance. Calling a method on a pointer will almost always be faster than copying the value. There may be cases wear the copy is faster but those are edge case.
2. Consistency. It is common for at least one of your methods to need a pointer receiver and if any of the type’s methods are on the pointer then they all should be. This recommendation is direct from the FAQ.

Read the FAQ “Should I define methods on values or pointers?” for more insight.

Update: Thanks to the fine folks on reddit for suggesting some improvements.
Join the discussion on reddit!

Update 2: Here are even more rules of thumb to help you choose whether to use a value or pointer receiver.