Go Pointers: When to Use `&` and `*`?

Understanding Pointers (& and *)

Go often requires passing variables as arguments to functions. However, it can be confusing when encountering errors during such operations. This article clarifies the difference between & and * pointers, explaining when each should be used.

Pointers and Addresses

Pointers are variables that store the address of another variable in memory. The & operator retrieves the address of a variable. For example, if 'u' is a User struct, '&u' returns the address of 'u'.

Decoding JSON with &

To understand the & operator, consider the following code:

var u User

if err := decoder.Decode(&u); err != nil {
    // Code to handle error...
}

The json.Decode function expects a pointer to decode the JSON data into. In this example, 'u' is only a User struct, not a pointer. By using '&u', we provide the function with the address of 'u', allowing the decoding to succeed.

Pointers and Redirection

The operator can be thought of as a "redirection" to the value stored at the address of a pointer. For instance, if pointer 'x' stores the address of 'y', 'x' gives us the value of 'y'.

Consider the following code:

x := new(User) // Creates a pointer to a User struct
*x = y        // Assigns the value of 'y' to the struct pointed to by 'x'
fmt.Println(*x) // Prints the value of 'y'

Summary of Usage

• Use & to obtain the address of a variable or to pass a pointer to a function that requires one.
• Use * to access the value stored at the address of a pointer.
• Avoid using * on non-pointers, as it will result in an error.

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