strings.IndexFunc() Function in Golang With Examples

strings.IndexFunc() Function in Golang is used to returns the index into s of the first Unicode code point satisfying f(c), or -1 if none do.

Syntax:

func IndexFunc(str string, f func(rune) bool) int

Here, str is string which may contain Unicode code point and f is func which validates the Unicode point.

Return Value: It returns the index of the first Unicode code point satisfying func.

Example 1:

// Golang program to show the usage
// of strings.IndexFunc() Function
package main

// importing fmt, unicode and strings
import (
    "fmt"
    "strings"
    "unicode"
)

func main() {

    // func f which validates the Greek 
    // Unicode character in the string
    f := func(c rune) bool {
        return unicode.Is(unicode.Greek, c)
    }
    
    // using the function
    fmt.Println(strings.IndexFunc("Hello Geeks!α", f)) 
}

Output:

13

Example 2:

// Golang program to show the usage
// of strings.IndexFunc() Function
package main

// importing fmt, unicode and strings
import (
    "fmt"
    "strings"
    "unicode"
)

func main() {

    // func f which validates the Greek
    // Unicode character in the string
    f := func(c rune) bool {
        return unicode.Is(unicode.Greek, c)
    }

    // using the function
    fmt.Println(strings.IndexFunc("GeeksforGeeks", f))
}

Output:

-1