Add slice Splice an element or multiple elements at index i.

[wenlingang]

Inserts an element or multiple elements at index i.

[1800alex]

This code looks good to me, anything preventing this from being merged? Would like to make use of it

[1800alex]

On second glance, something seems off

package slices

import (
	"testing"
)

// Insert inserts an element at index i.
// Play: https://go.dev/play/p/Eu3pk6_ODVQ
func Insert[T any](collection []T, i int, element T) []T {
	result := make([]T, len(collection)+1)
	copy(result, collection[:i])
	result[i] = element
	copy(result[i+1:], collection[i:])

	return result
}

// Insert inserts an element at index i.
func Insert2[T any](collection []T, i int, element T) []T {
	return append(collection[:i], append([]T{element}, collection[i:]...)...)
}

func BenchmarkInsertSlice(b *testing.B) {
	data := make([]int, 0)
	for i := 0; i < b.N; i++ {
		data = Insert(data, i, i)
	}
}

func BenchmarkInsertSlice2(b *testing.B) {
	data := make([]int, 0)
	for i := 0; i < b.N; i++ {
		data = Insert2(data, i, i)
	}
}

Running a benchmark of this seems way off from how I would expect an insert to look.

goos: linux
goarch: amd64
pkg: slices
cpu: AMD Ryzen 9 7900X 12-Core Processor
BenchmarkInsertSlice-24           153384            112324 ns/op
BenchmarkInsertSlice2-24        189345357                6.104 ns/op

[wenlingang]

On second glance, something seems off

package slices

import (
	"testing"
)

// Insert inserts an element at index i.
// Play: https://go.dev/play/p/Eu3pk6_ODVQ
func Insert[T any](collection []T, i int, element T) []T {
	result := make([]T, len(collection)+1)
	copy(result, collection[:i])
	result[i] = element
	copy(result[i+1:], collection[i:])

	return result
}

// Insert inserts an element at index i.
func Insert2[T any](collection []T, i int, element T) []T {
	return append(collection[:i], append([]T{element}, collection[i:]...)...)
}

func BenchmarkInsertSlice(b *testing.B) {
	data := make([]int, 0)
	for i := 0; i < b.N; i++ {
		data = Insert(data, i, i)
	}
}

func BenchmarkInsertSlice2(b *testing.B) {
	data := make([]int, 0)
	for i := 0; i < b.N; i++ {
		data = Insert2(data, i, i)
	}
}

Running a benchmark of this seems way off from how I would expect an insert to look.

goos: linux
goarch: amd64
pkg: slices
cpu: AMD Ryzen 9 7900X 12-Core Processor
BenchmarkInsertSlice-24           153384            112324 ns/op
BenchmarkInsertSlice2-24        189345357                6.104 ns/op

Thank you. After testing, it is indeed as you said, and I modified it again, this is my test result

goos: darwin
goarch: arm64

BenchmarkInsert-8 100000000 13.07 ns/op
BenchmarkInsertSlice-8 202900190 11.44 ns/op

[samber]

Wow, the difference between both versions is impressive!

Sorry for the delay.

I like your helper, but I'm not sure calling it Insert is self-explanatory.

JS, PHP, C++ and Rust named it "splice".

[samber]

And I think we should leverage vaargs to write a single helper instead of 2.

[wenlingang]

@samber Thank you for your suggestion. I found that it can be further optimized, and I have already done it. Additionally, the name 'Insert' is borrowed from Ruby's Array#insert, though 'Splice' is also a good name.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 28.57143% with 5 lines in your changes missing coverage. Please review.

Project coverage is 94.12%. Comparing base (89ca7c6) to head (0066bed).
Report is 1 commits behind head on master.

Files	Patch %	Lines
slice.go	28.57%	3 Missing and 2 partials ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #371      +/-   ##
==========================================
- Coverage   94.30%   94.12%   -0.18%     
==========================================
  Files          17       17              
  Lines        2633     2640       +7     
==========================================
+ Hits         2483     2485       +2     
- Misses        148      151       +3     
- Partials        2        4       +2     

Flag	Coverage Δ
unittests	94.12% <28.57%> (-0.18%)	⬇️

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[samber]

Suggested change

	func TestInsertSlice(t *testing.T) {
	func TestSplice(t *testing.T) {

[samber]

I made some changes:

• handle overflow
• negative index
• insert into newly allocated slice instead of append()