https://github.com/m0t9/arrcopy

Go linter prohibiting for-range over arrays copies
https://github.com/m0t9/arrcopy

go linter optimization performance-tuning

Last synced: 22 days ago
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Go linter prohibiting for-range over arrays copies

• Host: GitHub
• URL: https://github.com/m0t9/arrcopy
• Owner: m0t9
• License: mit
• Created: 2025-01-03T16:53:36.000Z (25 days ago)
• Default Branch: master
• Last Pushed: 2025-01-04T19:01:17.000Z (24 days ago)
• Last Synced: 2025-01-04T19:29:40.779Z (24 days ago)
• Topics: go, linter, optimization, performance-tuning
• Language: Go
• Homepage:
• Size: 10.7 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# arrcopy

[![coverage](https://raw.githubusercontent.com/m0t9/arrcopy/badges/.badges/master/coverage.svg)](https://github.com/m0t9/arrcopy/actions/workflows/.testcoverage.yml)

[![build](https://github.com/m0t9/arrcopy/actions/workflows/go.yml/badge.svg)](https://github.com/m0t9/arrcopy/actions/workflows/go.yml)

Simple Go linter prohibiting `for-range` iteration over array copy.

## Details

The `range` operator creates a copy of the array before iterating over it.

In case of heavyweight arrays it may lead to significant performance degradation.

One can see explanation with clear benchmarks [here](https://medium.com/@haaawk/i-thought-i-understood-how-iteration-over-an-array-works-but-apparently-not-in-golang-441a7abd6540)

## Usage

### Installation

`go install github.com/m0t9/arrcopy/cmd/...@latest`

### Running

Linter is compatible with `go vet`

`go vet -vettool=$(which arrcopy) ./...` 

## Optimization example 

The inefficiency of array copying can be shown in the benchmark below

```go

func BenchmarkArrayIteration(b *testing.B) {

	const Size = 1000000

	type Item struct {

		s      string

		subarr [5]int64

		sl     []int

		p      *int

	}

	b.Run("over copy", func(b *testing.B) {

		for i := 0; i < b.N; i++ {

			b.StopTimer()

			arr := [Size]Item{}

			b.StartTimer()

			for idx, item := range arr {

				_, _ = idx, item

			}

		}

	})

	b.Run("over reference", func(b *testing.B) {

		for i := 0; i < b.N; i++ {

			b.StopTimer()

			arr := [Size]Item{}

			b.StartTimer()

			for idx, item := range &arr { // added & before arr

				_, _ = idx, item

			}

		}

	})

}

```

```

goos: darwin

goarch: arm64

pkg: github.com/m0t9/arrcopy/cmd/arrcopy

cpu: Apple M1

BenchmarkArrayIteration/over_copy-8                   52          21382312 ns/op

BenchmarkArrayIteration/over_reference-8            3085            382052 ns/op

PASS

ok      github.com/m0t9/arrcopy/cmd/arrcopy     9.923s

```