regex - What is the difference between regexp.Compile and regexp.CompilePOSIX? -

can provide examples explain differences between regexp.compile , regexp.compileposix? read documentation. can't intuitive understanding.

perl- , posix-compatible regular expressions similar in large parts, differ in key aspects, example submatching. mentioned here:

posix defines resolve submatches, first chose match starts leftmost in string. (this traditional perl behavior here things diverge.) among submatches starting @ leftmost position in string, choose longest 1 overall.

say have regular expression (foo|foobar). when matching expression against string match several of subexpressions (for example, foobarbaz match both subpatterns, foo , foobar), perl-compatible regex return first match (foo), while posix-compatible regex return longest match (foobar).

some example code (playground):

package main  import "fmt" import "regexp"  func main() {     pattern := "(foo|foobar)"     str := []byte("foobarbaz")      rpcre, _ := regexp.compile(pattern)     rposix, _ := regexp.compileposix(pattern)      matchespcre := rpcre.find(str)     fmt.println(string(matchespcre))     // prints "foo"      matchesposix := rposix.find(str)     fmt.println(string(matchesposix))     // prints "foobar" }