Use strings.Contains instead of strings.Index with -1

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Metadata

ID: go-best-practices/strings-index-contains

Language: Go

Severity: Notice

Category: Best Practices

Description

In Go, when checking if one string contains another string, it is recommended to use strings.Contains(x, y) instead of strings.Index(x, y) != -1.

Here are the reasons why strings.Contains(x, y) is preferred:

Simplicity and Readability: Using strings.Contains(x, y) provides a more readable and expressive way to check if a string x contains another string y. It clearly conveys the intention of the condition without needing an additional comparison operator.
Performance: strings.Contains(x, y) is optimized for efficiency and performance. It uses an optimized implementation to check for substring presence, avoiding the need to search for the index and perform an additional comparison.
Avoiding Errors: When using strings.Index(x, y), you need to compare against -1 to check for absence, which can be error-prone. Mistakenly using 0 instead of -1 would lead to incorrect results. Using strings.Contains(x, y) eliminates the possibility of such mistakes.

For example, consider the following code snippets:

1
2
3
if strings.Contains(x, y) {
    // Code block
}

1
2
3
if strings.Index(x, y) != -1 {
    // Code block
}

Both snippets check if the string x contains the substring y. However, the first snippet using strings.Contains(x, y) is preferred for its simplicity, readability, and performance benefits.

By using strings.Contains(x, y) instead of strings.Index(x, y) != -1, you can write cleaner and more efficient code that adheres to Go’s idiomatic style.

Non-Compliant Code Examples

import (
	"fmt"
	str2 "strings"
)

func main () {
    if str2.Index(x, y) != -1 {
        //
    }
}

import (
	"fmt"
	"strings"
)

func main () {
    if strings.Index(x, y) != -1 {
        //
    }
}

Compliant Code Examples

import (
	"fmt"
	"strings"
)

func main () {
    if strings.Contains(x, y) {
        //
    }
}