Passing by Value in Functions

In this lesson, we explore the concept of passing arguments by value in functions. There are two primary methods for passing arguments: passing by value and passing by reference. In this guide, our focus is on passing by value.

Passing by value means that when you pass a variable to a function, its value is copied to a new memory location. Any modifications made to the parameter within the function affect only the copy, leaving the original variable unchanged. Basic data types such as integers, floats, booleans, and strings are all passed by value.

Memory Layout Example

Consider a scenario where a variable a is declared inside the main function. The variable a is stored in memory at a particular address. When a is passed to the function modify, the value is copied to another memory location. As a result, any modification within modify does not impact the original value of a.

Imagine a memory layout as shown below:

memory address     memory
0x0301            10
0x0302
0x0303
0x0304
0x0305
0x0306

In this example, when the function adds 100 to the copy of the variable, the original value of a remains 10.

Go Code Example: Integers

Below is a Go code snippet that demonstrates passing by value with integer data:

package main

import "fmt"

func modify(a int) {
    a += 100
}

func main() {
    a := 10
    fmt.Println(a) // Output: 10
    modify(a)
    fmt.Println(a) // Output: 10, since a is passed by value
}

As shown, the original value of a remains unchanged after the modify function is called.

Go Code Example: Strings

Now consider an example with a string. In this case, a string variable is created with the value "hello". The string is printed, passed to a function called modify that attempts to change its value to "world", and then printed again. Despite the change within the function, the original string remains "hello" because it was passed by value.

package main

import "fmt"

func modify(s string) {
    s = "world"
}

func main() {
    a := "hello"
    fmt.Println(a) // Output: hello
    modify(a)
    fmt.Println(a) // Output: hello, since s is only a copy of a
}

Console output:

>>> go run main.go
hello
hello

In this case, the parameter s inside the modify function is simply a copy of the variable a. Thus, when s is updated to "world", the original variable a remains unchanged.

That concludes our lesson on passing by value in functions. In the next lesson, we will continue exploring more advanced programming concepts.