add lazy loading

pkg/rules/regex.go

@@ -0,0 +1,34 @@
+package rules
+
+import (
+	"regexp"
+	"sync"
+)
+
+// nolint: lll
+// Define all regular expressions here:
+var (
+	validUUIDRegexp = lazyRegexCompile(`^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$`)
+	asciiRegexp     = lazyRegexCompile(`^[\x00-\x7F]*$`)
+)
+
+// lazyRegexCompile returns a function that compiles the regular expression
+// once, when the function is called for the first time.
+// If the function is never called, the regular expression is never compiled,
+// thus saving on performance.
+//
+// All regular expression literals should be compiled using this function.
+//
+// Credits: https://github.com/go-playground/validator/commit/2e1df48b5ab876bdd461bdccc51d109389e7572f
+func lazyRegexCompile(str string) func() *regexp.Regexp {
+	var (
+		regex *regexp.Regexp
+		once  sync.Once
+	)
+	return func() *regexp.Regexp {
+		once.Do(func() {
+			regex = regexp.MustCompile(str)
+		})
+		return regex
+	}
+}

pkg/rules/string.go

@@ -73,24 +73,19 @@ func StringDNSLabel() govy.RuleSet[string] {
 	).WithErrorCode(ErrorCodeStringDNSLabel)
 }
 
-var validUUIDRegexp = regexp.
-	MustCompile("^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$")
-
 // StringUUID ensures property's value is a valid UUID string.
 func StringUUID() govy.Rule[string] {
-	return StringMatchRegexp(validUUIDRegexp,
+	return StringMatchRegexp(validUUIDRegexp(),
 		"00000000-0000-0000-0000-000000000000",
 		"e190c630-8873-11ee-b9d1-0242ac120002",
 		"79258D24-01A7-47E5-ACBB-7E762DE52298").
 		WithDetails("expected RFC-4122 compliant UUID string").
 		WithErrorCode(ErrorCodeStringUUID)
 }
 
-var asciiRegexp = regexp.MustCompile("^[\x00-\x7F]*$")
-
 // StringASCII ensures property's value contains only ASCII characters.
 func StringASCII() govy.Rule[string] {
-	return StringMatchRegexp(asciiRegexp).WithErrorCode(ErrorCodeStringASCII)
+	return StringMatchRegexp(asciiRegexp()).WithErrorCode(ErrorCodeStringASCII)
 }
 
 // StringURL ensures property's value is a valid URL as defined by [url.Parse] function.