replacing placeholders in a template faster than (strings|bytes).replace / regexp.ReplaceAllStringFunc
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STATUS: While it still works as advertised, this package is not maintained any longer in favor of which is a rewrite based on the same idea with a much simpler usage and it is even a bit faster.

Build Status

The typical scenario is that your template never changes but the replacements for you placeholders. fastreplace is faster than using (strings|bytes).Replace or regexp.ReplaceAllStringFunc in this situation.


Run benchmarks in benchmark directory. I get the following results on my laptop:

replacing 2 placeholders that occur 2500x in the template

BenchmarkNaive	         500	 3759998 ns/op    2.5x (strings.Replace)
BenchmarkReg	         100	25826150 ns/op   17.1x (regexp.ReplaceAllStringFunc)
BenchmarkByte	        1000	 2862196 ns/op    1.9x (bytes.Replace)
BenchmarkFReplace	    1000	 2115185 ns/op    1.4x
BenchmarkFReplacePos	1000	 1513158 ns/op    1.0x

replacing 5000 placeholders that occur 1x in the template

BenchmarkNaiveM	           1  5494931000 ns/op 3652.1x (strings.Replace)
BenchmarkRegM	          50	29896260 ns/op	 19.9x (regexp.ReplaceAllStringFunc)
BenchmarkByteM	           1  3881286000 ns/op 2579.7x (bytes.Replace)
BenchmarkFReplaceM	    1000     2368541 ns/op	  1.6x
BenchmarkFReplacePosM	1000	 1504577 ns/op	  1.0x

replacing 2 placeholders that occur 1x in the template, parsing template each time (you should not do this)

BenchmarkNaiveOneShot	 500	 3756994 ns/op	  1.3x (strings.Replace)
BenchmarkOneShotReg	     100    25417730 ns/op	  8.6x (regexp.ReplaceAllStringFunc)
BenchmarkOneShotByte    1000	 2941726 ns/op	  1.0x (bytes.Replace)
BenchmarkFReplaceOneShot 200	 7813775 ns/op	  2.7x


package main

import (

var r, _ = fastreplace.NewString("@@", "@@name@@ / @@city@@")
var posCity = r.Pos("city")[0]
var posName = r.Pos("name")[0]

func main() {
	i := map[string][]byte{
		"city": []byte("Armonk"),
		"name": []byte("IBM"),

	// more comfort
	m := r.Instance()
	m.AssignString("city", "Redmond")
	m.AssignString("name", "Microsoft")

	fmt.Println(r.ReplaceString(i), " - ", m)

	// to be even faster (FReplacePos in the benchmarks)
	// you could cache the positions of the needed placeholders (see merg func below)
		string(merge([]byte("Google"), []byte("Mountain View"))),
		" - ",
		string(merge([]byte("Apple"), []byte("Cupertino"))),

func merge(name []byte, city []byte) []byte {
	m := map[int][]byte{posCity: city, posName: name}
	return r.ReplacePosBytes(m)

results in

IBM / Armonk  -  Microsoft / Redmond
Google / Mountain View  -  Apple / Cupertino