Benchmark deleting the parts of a slice, for various slice lengths

delete_test.go

package delete

import (
	"fmt"
	"testing"

	"golang.org/x/exp/slices"
)

func BenchmarkDeleteLast(b *testing.B) {
	for k := 10; k < 10_000_000; k *= 10 {
		name := fmt.Sprintf("DeleteLast_1_%d", k)
		b.Run(name, func(b *testing.B) {
			s := make([]byte, k)
			b.ResetTimer()
			for i := 0; i < b.N; i++ {
				Sink = slices.Delete(s, k-1, k)
			}
		})
	}
}

func BenchmarkDeleteLast1000(b *testing.B) {
	for k := 1000; k < 10_000_000; k *= 10 {
		name := fmt.Sprintf("DeleteLast_1000_%d", k)
		b.Run(name, func(b *testing.B) {
			s := make([]byte, k)
			b.ResetTimer()
			for i := 0; i < b.N; i++ {
				Sink = slices.Delete(s, k-1, k)
			}
		})
	}
}

func BenchmarkDeleteMiddle(b *testing.B) {
	for k := 10; k < 10_000_000; k *= 10 {
		name := fmt.Sprintf("DeleteMiddle_1_%d", k)
		b.Run(name, func(b *testing.B) {
			s := make([]byte, k)
			m := k / 2
			b.ResetTimer()
			for i := 0; i < b.N; i++ {
				Sink = slices.Delete(s, m, m+1)
			}
		})
	}
}

// Prevent optimizing things away
var Sink []byte

Results on my workstation:

% go test -bench=.
goos: darwin
goarch: amd64
pkg: delete
cpu: VirtualApple @ 2.50GHz
BenchmarkDeleteLast/DeleteLast_1_10-10         	300007938	         4.004 ns/op
BenchmarkDeleteLast/DeleteLast_1_100-10        	299902094	         4.002 ns/op
BenchmarkDeleteLast/DeleteLast_1_1000-10       	300838335	         3.991 ns/op
BenchmarkDeleteLast/DeleteLast_1_10000-10      	301185762	         3.996 ns/op
BenchmarkDeleteLast/DeleteLast_1_100000-10     	300077894	         3.998 ns/op
BenchmarkDeleteLast/DeleteLast_1_1000000-10    	301128510	         4.107 ns/op
BenchmarkDeleteLast1000/DeleteLast_1000_1000-10         	296975397	         3.999 ns/op
BenchmarkDeleteLast1000/DeleteLast_1000_10000-10        	299375800	         4.025 ns/op
BenchmarkDeleteLast1000/DeleteLast_1000_100000-10       	300890383	         4.006 ns/op
BenchmarkDeleteLast1000/DeleteLast_1000_1000000-10      	300420024	         4.008 ns/op
BenchmarkDeleteMiddle/DeleteMiddle_1_10-10              	225945192	         5.314 ns/op
BenchmarkDeleteMiddle/DeleteMiddle_1_100-10             	218974356	         5.431 ns/op
BenchmarkDeleteMiddle/DeleteMiddle_1_1000-10            	96280815	        12.51 ns/op
BenchmarkDeleteMiddle/DeleteMiddle_1_10000-10           	 5246284	       228.0 ns/op
BenchmarkDeleteMiddle/DeleteMiddle_1_100000-10          	  542217	      2215 ns/op
BenchmarkDeleteMiddle/DeleteMiddle_1_1000000-10         	   53709	     22304 ns/op
PASS
ok  	delete	25.773s

The first part DeleteLast shows that deleting the end of a slice is constant time, regardless the size of the slice, and regardless the number of elements to delete.

The second part DeleteMiddle is consistent with the amount of work needed to shift half of the slice to the left, which is O(len(s)-j).