Pointers explained

yourbasic.org/golang

A pointer is a vari­able that con­tains the address of an object.

Basics

Structs and arrays are copied when used in assignments and passed as arguments to functions. With pointers this can be avoided.

Pointers store addresses of objects. The addresses can be passed around more efficiently than the actual objects.

A pointer has type *T. The keyword new allocates a new object and returns its address.

type Student struct {
    Name string
}

var ps *Student = new(Student) // ps holds the address of the new struct

The variable declaration can be written more compactly.

ps := new(Student)

Address operator

The & operator returns the address of an object.

s := Student{"Alice"} // s holds the actual struct 
ps := &s              // ps holds the address of the struct 

The & operator can also be used with composite literals. The two lines above can be written as

ps := &Student{"Alice"}

Pointer indirection

For a pointer x, the pointer indirection *x denotes the value which x points to. Pointer indirection is rarely used, since Go can automatically take the address of a variable.

ps := new(Student)
ps.Name = "Alice" // same as (*ps).Name = "Alice"

Pointers as parameters

When using a pointer to modify an object, you’re affecting all code that uses the object.

// Bob is a function that has no effect.
func Bob(s Student) {
    s.Name = "Bob" // changes only the local copy
}

// Charlie sets pp.Name to "Charlie".
func Charlie(ps *Student) {
    ps.Name = "Charlie"
}

func main() {
    s := Student{"Alice"}

    Bob(s)
    fmt.Println(s) // prints {Alice}

    Charlie(&s)
    fmt.Println(s) // prints {Charlie}
}

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