Capturing Groups in Go Regular Expressions

In Go, regular expressions utilize the RE2 library, which lacks native support for capturing groups as found in Ruby and other languages. However, there is a solution to emulate this functionality.

To achieve the desired behavior, one needs to append "P" to the group name, as illustrated in the following updated expression:

(?P\d{4})-(?P\d{2})-(?P\d{2})

To extract the values from the capturing groups, one can employ the re.SubexpNames() function to obtain the group names and cross-reference them with the match data.

Consider the following example:

package main

import (
    "fmt"
    "regexp"
)

func main() {
    r := regexp.MustCompile(`(?P\d{4})-(?P\d{2})-(?P\d{2})`)
    fmt.Printf("%#v\n", r.FindStringSubmatch(`2015-05-27`))
    fmt.Printf("%#v\n", r.SubexpNames())
}

In this example, r.FindStringSubmatch() returns the matching substring and the corresponding r.SubexpNames() provides the group names:

[]string{"2015", "05", "27"}
[]string{"", "Year", "Month", "Day"}

Thus, one can conveniently access the captured year, month, and day using group names, offering similar functionality to capturing groups in other languages.