The value of a variable can be passed to a function in several ways:

• Value: A copy of the variable’s value is passed so that the function can work with it in its local scope.
• Reference: The memory address (pointer) where the variable is located is passed, making it a “shared” variable.

If you’re new to the Go world, I recommend the following previous articles:

• Go basics
• Go functions
• Go unit tests

In Go, to obtain the memory address of a variable, we will refer to it as follows:

&VARIABLE_NAME

If a function is going to receive a variable as input that should be a pointer, we will define it as follows:

func zeroptr(iptr *int) {

In this simple example, we can see two functions, zeroval, which receives the value of the variable i by copy, and the function zeroptr, which receives it by reference:

package main

import "fmt"

func zeroval(ival int) {
    ival = 0
}

func zeroptr(iptr *int) {
    *iptr = 0
}

func main() {
    i := 1
    fmt.Println("i value:", i)

    zeroval(i)
    fmt.Println("i value:", i)

    zeroptr(&i)
    fmt.Println("i value:", i)

    fmt.Println("Memory address i variable:", &i)
}

When running the code, we get the following output:

i value: 1
i value: 1
i value: 0
Memory address i variable: 0x84c01c0a8

We can see that the value of the variable i in the main function has only been affected when we passed the pointer, as we have turned it into a “shared” variable between the main function and zeroptr.