golang append only vs make

main.go

package main

func plainAppend(elms int) {
	var foo []int
	for i := 0; i < elms; i++ {
		foo = append(foo, i)
	}
}

func withMake(elms int) {
	foo := make([]int, 0, elms)
	for i := 0; i < elms; i++ {
		foo = append(foo, i)
	}
}

main_test.go

package main

import "testing"

func Benchmark10(b *testing.B) {
	const elmCount = 10
	// iterations are controlled via -benchtime=Nx

	b.Run("append", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			plainAppend(elmCount)
		}
	})

	b.Run("with make", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			withMake(elmCount)
		}
	})
}

func Benchmark100(b *testing.B) {
	const elmCount = 100
	// iterations are controlled via -benchtime=Nx

	b.Run("append", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			plainAppend(elmCount)
		}
	})

	b.Run("with make", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			withMake(elmCount)
		}
	})
}

func Benchmark1k(b *testing.B) {
	const elmCount = 1000
	// iterations are controlled via -benchtime=Nx

	b.Run("append", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			plainAppend(elmCount)
		}
	})

	b.Run("with make", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			withMake(elmCount)
		}
	})
}

func Benchmark10k(b *testing.B) {
	const elmCount = 10000
	// iterations are controlled via -benchtime=Nx

	b.Run("append", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			plainAppend(elmCount)
		}
	})

	b.Run("with make", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			withMake(elmCount)
		}
	})
}

func Benchmark100k(b *testing.B) {
	const elmCount = 100_000
	// iterations are controlled via -benchtime=Nx

	b.Run("append", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			plainAppend(elmCount)
		}
	})

	b.Run("with make", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			withMake(elmCount)
		}
	})
}

func Benchmark1Million(b *testing.B) {
	const elmCount = 1000 * 1000
	// iterations are controlled via -benchtime=Nx

	b.Run("append", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			plainAppend(elmCount)
		}
	})

	b.Run("with make", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			withMake(elmCount)
		}
	})
}

result.txt

$ go test -bench=. -count=10 -benchtime=100x > bench.out

# https://godoc.org/golang.org/x/perf/cmd/benchstat
$ benchstat bench.out

name                  time/op
10/append-8            729ns ±62%
10/with_make-8         119ns ±84%
100/append-8          1.46µs ±84%
100/with_make-8        454ns ±99%
1k/append-8           5.28µs ±33%
1k/with_make-8        2.61µs ±54%
10k/append-8           111µs ±23%
10k/with_make-8       31.4µs ±11%
100k/append-8         1.16ms ± 8%
100k/with_make-8       248µs ±11%
1Million/append-8     8.57ms ± 3%
1Million/with_make-8  2.83ms ± 1%