How Does Go\'s `append()` Function Affect Slice Behavior When Passed by Value?

Understanding Append() Behavior on Slices

When working with slices in Go, it's important to understand how the append() function interacts with slices passed by value.

Consider the following code snippet:

func main() {
    slice := make([]int, 10, 10)
    slice[0] = 0
    slice[1] = 1

    slice1 := slice
    slice1[0] = 10000
    fmt.Println(slice)

    slice1 = append(slice1, 100)
    slice1[0] = 20000

    fmt.Println(slice)
}

In this example, two slices (slice and slice1) are created, with slice1 initially pointing to the same array as slice. However, after the first append() call, slice1 is assigned a new slice value that points to a different array. This assignment results in slice1's behavior being independent of slice.

Explanation:

• Pass by value: In Go, everything is passed by value, which means that slice1 receives a copy of slice's slice header.
• Append with capacity: When appending more than 0 elements to a slice with capacity equal to its length (as in this case), a new, larger array is allocated.
• Slice header assignment: The append() call returns a new slice header pointing to the new array, which is assigned to slice1.
• Independent slices: After the assignment, slice and slice1 become two distinct variables pointing to different slice headers and, therefore, different arrays.

Consequences:

• Immutability: Changes made to elements in one slice (e.g., slice1) will not be reflected in the other slice (e.g., slice).
• Memory management: Append operations can lead to memory reallocation, creating new arrays and potentially affecting performance.

To understand slice headers and their internals, refer to the following resources:

• [Are golang slices pass by value?](https://stackoverflow.com/questions/25740338/are-golang-slices-pass-by-value)
• [Go Slices: usage and internals](https://blog.golang.org/slices)

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