标签：POSIX match Regexp leftmost matching CompilePOSIX longest

// Copy returns a new Regexp object copied from re.
// Calling Longest on one copy does not affect another.
//
// Deprecated: In earlier releases, when using a Regexp in multiple goroutines,
// giving each goroutine its own copy helped to avoid lock contention.
// As of Go 1.12, using Copy is no longer necessary to avoid lock contention.
// Copy may still be appropriate if the reason for its use is to make
// two copies with different Longest settings.
func (re *Regexp) Copy() *Regexp {
re2 := *re
return &re2
}

// Compile parses a regular expression and returns, if successful,
// a Regexp object that can be used to match against text.
//
// When matching against text, the regexp returns a match that
// begins as early as possible in the input (leftmost), and among those
// it chooses the one that a backtracking search would have found first.
// This so-called leftmost-first matching is the same semantics
// that Perl, Python, and other implementations use, although this
// package implements it without the expense of backtracking.
// For POSIX leftmost-longest matching, see CompilePOSIX.
func Compile(expr string) (*Regexp, error) {
return compile(expr, syntax.Perl, false)
}

// CompilePOSIX is like Compile but restricts the regular expression
// to POSIX ERE (egrep) syntax and changes the match semantics to
// leftmost-longest.
//
// That is, when matching against text, the regexp returns a match that
// begins as early as possible in the input (leftmost), and among those
// it chooses a match that is as long as possible.
// This so-called leftmost-longest matching is the same semantics
// that early regular expression implementations used and that POSIX
// specifies.
//
// However, there can be multiple leftmost-longest matches, with different
// submatch choices, and here this package diverges from POSIX.
// Among the possible leftmost-longest matches, this package chooses
// the one that a backtracking search would have found first, while POSIX
// specifies that the match be chosen to maximize the length of the first
// subexpression, then the second, and so on from left to right.
// The POSIX rule is computationally prohibitive and not even well-defined.
// See https://swtch.com/~rsc/regexp/regexp2.html#posix for details.
func CompilePOSIX(expr string) (*Regexp, error) {
return compile(expr, syntax.POSIX, true)
}

标签：POSIX,match,Regexp,leftmost,matching,CompilePOSIX,longest
来源： https://www.cnblogs.com/rsapaper/p/14734663.html

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