How Do I Efficiently Clear a Slice in Go?

Efficiently Clearing a Slice in Go

In Go, a slice is a dynamically-sized pointer to a sequence of elements. To efficiently clear a slice, we explore different approaches and their implications.

Approach 1: Setting to nil**

Setting the slice to nil deallocates the underlying memory and resets the capacity to zero. This is the recommended approach as it:

• Releases memory resources for immediate garbage collection.
• Ensures the slice is in a predictable and "empty" state.
• Effectively "unaliases" the slice from any other references to the same underlying memory.

func main() {
    letters := []string{"a", "b", "c", "d"}
    fmt.Println(cap(letters)) // 4
    fmt.Println(len(letters)) // 4
    letters = nil             // Clear the slice
    fmt.Println(cap(letters)) // 0
    fmt.Println(len(letters)) // 0
}

Approach 2: Slicing to Zero Length

Another option is to slice the slice to a zero length, using the syntax [:0]. While this may appear to clear the slice, it actually:

• Retains the underlying memory.
• Reduces the slice's length to zero, but not its capacity.
• May lead to unexpected behavior if the slice is later referenced.

func main() {
    letters := []string{"a", "b", "c", "d"}
    fmt.Println(cap(letters)) // 4
    fmt.Println(len(letters)) // 4
    letters = letters[:0]     // Slice to zero length
    fmt.Println(cap(letters)) // 4
    fmt.Println(len(letters)) // 0
}

Best Practice

Setting the slice to nil is the preferred approach for clearing a slice in Go, as it effectively deallocates memory and prevents any potential aliasing issues.

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