How Can I Effectively Modify Slices Passed as Arguments in Go?

Pass Slices Effectively in Go: Avoid Value Pass Limitations

In Go, passing a slice as a function argument is essentially done by value. This implies that if an argument slice is modified within the function using append, it will not affect the original slice outside the function's scope.

To illustrate this limitation, consider the following example:

nums := []int{1, 2, 3}

func addToNumbs(nums []int) []int {
    nums = append(nums, 4)
    fmt.Println(nums) // []int{1, 2, 3, 4}
}

fmt.Println(nums) // []int{1, 2, 3}

In this example, the original slice nums remains unaffected despite the modification within the addToNumbs function. To resolve this issue, one can pass a pointer to the slice instead:

func myAppend(list *[]string, value string) {
    *list = append(*list, value)
}

This approach ensures that the original slice is modified directly.

Alternatively, in certain scenarios, simply returning the modified slice from the function can be an efficient solution:

func validate(obj Validatable, messages []ValidationMessage) ([]ValidationMessage, error) {
    // Modification...
    return messages, nil
}

In summary, when passing a slice as an argument in Go, it's crucial to consider whether modifications within the function should impact the original slice. If so, utilizing a pointer to the slice or returning the modified slice are effective approaches to achieve the desired behavior.

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