Float64->String Conversions in Go

conv.go

package vals

import (
	"strings"
	"strconv"
	"fmt"
)


// SprintValues is a set of float64 values that implements Buckets.
type SprintValues []float64

func (v SprintValues) String() string {
	values := make([]string, len(v))
	for i := range values {
		values[i] = fmt.Sprintf("%f", v[i])
	}
	return fmt.Sprint(values)
}

type ConvValues []float64

func (v ConvValues) String() string {
	values := make([]string, len(v))
	for i := range values {
		values[i] = strconv.FormatFloat(v[i], 'f', 6, 64) // matches fmt formatting
	}
	return fmt.Sprint(values)
}

type BuildValues []float64

func (v BuildValues) String() string {
	var b strings.Builder
	b.WriteByte('[')
	for i := range v {
		fmt.Fprintf(&b, "%f", v[i])
		if i != len(v)-1{
			b.WriteByte(' ')
		}
	}
	b.WriteByte(']')
	return b.String()
}

conv_test.go

package vals

import (
	"runtime"
	"testing"
)

var sortArr []float64

func init() {
	sortArr = []float64{3.0,4.0,1.0,4.0,12.0,99999.000000001, 99999999.000002002}
	for i := 0; i < 16; i++ {
		sortArr = append(sortArr, sortArr...)
	}
}

func BenchmarkPrintf(b *testing.B) {
	b.ReportAllocs()
	bucket := SprintValues(sortArr)
	for i := 0; i < b.N; i++ {
		result := bucket.String()
		runtime.KeepAlive(result)
	}
}

func BenchmarkStrConv(b *testing.B) {
	b.ReportAllocs()
	bucket := ConvValues(sortArr)
	for i := 0; i < b.N; i++ {
		result := bucket.String()
		runtime.KeepAlive(result)
	}
}

func BenchmarkBuilder(b *testing.B) {
	b.ReportAllocs()
	bucket := BuildValues(sortArr)
	for i := 0; i < b.N; i++ {
		result := bucket.String()
		runtime.KeepAlive(result)
	}
}

func TestEquality(t *testing.T) {
	build := BuildValues(sortArr)
	val := SprintValues(sortArr)
	conv := ConvValues(sortArr)

	if build.String() != val.String() {
		t.Errorf("%s::%s", build.String(), val.String())
	}
	if val.String() != conv.String() {
		t.Errorf("%s::%s", val.String(), conv.String())
	}
	if conv.String() != build.String() {
		t.Errorf("%s::%s", conv.String(), build.String())
	}
	t.Log("Builder:", build.String())
	t.Log("Sprintf:", val.String())
	t.Log("Strconv:", conv.String())
}

results.md

BenchmarkPrintf-8    	       6	 187680616 ns/op	57351464 B/op	 1376303 allocs/op
BenchmarkStrConv-8   	       7	 173820460 ns/op	68361486 B/op	 1376303 allocs/op
BenchmarkBuilder-8   	       9	 121909527 ns/op	32507531 B/op	  458804 allocs/op

Not an order of magnitude faster, but the allocation savings alone is worth switching to a strings.Builder if you can.