Snippet

Efficient Slice Filtering Without Allocating New Memory

Filtering a slice in Go can be done in-place by reusing the backing array of the input slice. This avoids allocating a new slice on the heap and improves memory performance.

snippet.go

package main
 
import "fmt"
 
func filterEven(numbers []int) []int {
	n := 0
	for _, x := range numbers {
		if x%2 == 0 {
			numbers[n] = x
			n++
		}
	}
	return numbers[:n]
}
 
func main() {
	nums := []int{1, 2, 3, 4, 5, 6}
	filtered := filterEven(nums)
	fmt.Println("Filtered:", filtered)
	fmt.Println("Original backing array modified:", nums)
}

Breakdown

n := 0

Initializes an index tracker to write elements to the same underlying array.

numbers[n] = x

Overwrites the element at index `n` with the current matching element.

n++

Increments the index tracker to prepare for the next matching element.

return numbers[:n]

Returns a slice expression sharing the same backing array up to length `n`.

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Efficient Slice Filtering Without Allocating New Memory

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