String Replacements in Go

In a previous post, we saw how we can use Regular expressions in Go to match and replace patterns in a string. While regexps are very useful, you might not want to them for every time you want to do some basic string manipulation. The strings package has few functions which works well for basic string replacement.

Let’s look at two such functions.

strings.Replace

Just as the name suggests, this strings.Replace function does a very basic string replacement. This is the signature of this function.

func Replace(s, old, new string, n int) string

s is the string in which you want to replace old with new and the integer n tells how many occurences should be replaced. If n is < 0, all occurences will be replaced.

package main

import (
    "strings"
    "fmt"
)

const refString = "Apple is the most customer centric company. Apple is the first company to reach 1 Trillion market cap in the world."
func main() {
    out := strings.Replace(refString, "Apple", "Amazon", 1)
    fmt.Println(out)
}

As expected, this prints the following.

Amazon is the most customer centric company. Apple is the first company to reach 1 Trillion market cap in the world.

strings.NewReplacer

The strings.Replace works fine if you have only one string to replace. If you have multiple strings, you would need something more powerful. Thats why we have the strings.NewReplacer. The NewReplacer function takes in pairs of old:new strings and returns a new Replacer. You can call the Replace method on this struct to do a quick replacement on your string.

package main

import (
    "fmt"
    "strings"
)

func main() {
    r := strings.NewReplacer("<", "&lt;", ">", "&gt;")
    fmt.Println(r.Replace("This is <b>HTML</b>!"))
}

The advantage of using the strings.NewReplacer is that it uses an efficient data structure (called Trie) to do all the replacements in a single pass of the string. This is much faster if you have a lot of very basic string replacements.

However if you need to use various patterns to match, you are stuct with constructing and compiling your regular expression.

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