arrcopy

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

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

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