reonce

Package reonce provides lazy regexp initialization. This allows global regexp.Regexp variables to be used without incurring an initialization cost at startup (useful for CLIs).

The github.com/charlievieth/reonce/recache sub-package provides a thread-safe LRU regex cache.

Usage

The New() and NewPOSIX() functions return a lazily initialized *Regexp that thinly wraps *regexp.Regexp. The underlying regexp will not be compiled until used and will panic if there is a compilation error.

Lazy compilation is thread-safe and will panic if there is an error. This matches the behavior of regexp.MustCompile() and regexp.MustCompilePOSIX(). The panic messages are the same as those used by the standard library.

The Regexp.Compile() method can be used to manually force compilation or get the compilation error of a previously compiled Regexp, if any.

import "github.com/charlievieth/reonce"

// Define UUID regexes up-front, neither will be compiled until first use.

var uuidRe = reonce.New(
	`\b[[:xdigit:]]{8}-[[:xdigit:]]{4}-[[:xdigit:]]{4}-[[:xdigit:]]{4}-[[:xdigit:]]{12}\b`,
)

var uuidExactRe = reonce.New(
	`^[[:xdigit:]]{8}-[[:xdigit:]]{4}-[[:xdigit:]]{4}-[[:xdigit:]]{4}-[[:xdigit:]]{12}$`,
)

// ContainsUUID returns if string s contains a UUID.
func ContainsUUID(s string) bool {
	return uuidRe.MatchString(s)
}

// IsUUID returns if string s is a UUID.
func IsUUID(s string) bool {
	return uuidExactRe.MatchString(s)
}

Testing

The reoncetest build tag forces reonce to immediately compile regexes and panic on error. This useful for testing regexes that are initialized on program creation or any other *Regexp that is created, but not immediately used.

# use the `reoncetest` build tag when testing your code
$ go test -tags reoncetest ./...

This build tah should not be used in production/releases as it disables lazy compilation, which is the purpose of this package.

Overhead

Once compiled, the overhead of lazy compilation is a call to sync.Once.Do() which should be around ~2ns.

goos: darwin
goarch: arm64
pkg: github.com/charlievieth/reonce
BenchmarkInitOverhead-10                      	557014276	         2.173 ns/op
BenchmarkInitOverhead_Parallel-10             	1000000000	         0.2770 ns/op

goos: linux
goarch: amd64
pkg: github.com/charlievieth/reonce
cpu: Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz
BenchmarkInitOverhead-16                      	710212690	         1.624 ns/op
BenchmarkInitOverhead_Parallel-16             	1000000000	         0.3778 ns/op