refactor: update to functional options pattern

README.md

@@ -15,7 +15,7 @@ Usage
 func main() {
 	// Instantiate Parser with fields and patterns set
 	// The default is to return each matched line in NDJSON (newline-separated JSON) format
-	p := parser.New(fields, patterns, nil, nil)
+	p := parser.New(fields, patterns)
 
 	// Parses from a string passed
 	log := `dummy string`
@@ -69,7 +69,7 @@ Customize
 Processing of each matched line and metadata output can be overridden when Parser instantiation.
 
 ```go
-p := parser.New(fields, patterns, customLineHandler, customMetadataHandler)
+p := parser.New(fields, patterns, WithLineHandler(customLineHandler), WithMetadataHandler(customMetadataHandler))
 ```
 
 If you want to pretty-print json, you can wrap the default handler:
@@ -99,7 +99,7 @@ func prettyJSONMetadataHandler(m *parser.Metadata) (string, error) {
 	return prettyJSON(s)
 }
 
-p := parser.New(fields, patterns, prettyJSONLineHandler, prettyJSONMetadataHandler)
+p := parser.New(fields, patterns, WithLineHandler(prettyJSONLineHandler), WithMetadataHandler(prettyJSONMetadataHandler))
 ```
 
 Author

parser.go

@@ -68,20 +68,35 @@ type LineHandler func(matches []string, fields []string, index int) (string, err
 // MetadataHandler is a type for functions that process metadata.
 type MetadataHandler func(metadata *Metadata) (string, error)
 
-// New creates a new parser with the specified configurations.
-func New(fields []string, patterns []*regexp.Regexp, lineHandler LineHandler, metadataHandler MetadataHandler) *Parser {
-	if lineHandler == nil {
-		lineHandler = DefaultLineHandler
+// Option is an option to replace the behavior of LineHandler and MetadataHandler.
+type Option func(*Parser)
+
+// WithLineHandler overrides the behavior of DefaultLineHandler.
+func WithLineHandler(handler LineHandler) Option {
+	return func(p *Parser) {
+		p.LineHandler = handler
 	}
-	if metadataHandler == nil {
-		metadataHandler = DefaultMetadataHandler
+}
+
+// WithMetadataHandler overrides the behavior of DefaultMetadataHandler.
+func WithMetadataHandler(handler MetadataHandler) Option {
+	return func(p *Parser) {
+		p.MetadataHandler = handler
 	}
-	return &Parser{
+}
+
+// New creates a new parser with the specified configurations.
+func New(fields []string, patterns []*regexp.Regexp, opts ...Option) *Parser {
+	p := &Parser{
 		Fields:          fields,
 		Patterns:        patterns,
-		LineHandler:     lineHandler,
-		MetadataHandler: metadataHandler,
+		LineHandler:     DefaultLineHandler,
+		MetadataHandler: DefaultMetadataHandler,
+	}
+	for _, opt := range opts {
+		opt(p)
 	}
+	return p
 }
 
 // parse reads from the input, processes each line and returns parsed data and metadata.

parser_test.go

@@ -351,7 +351,14 @@ func TestNew(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			p := New(tt.args.fields, tt.args.patterns, tt.args.lineHandler, tt.args.metadataHandler)
+			opts := []Option{}
+			if tt.args.lineHandler != nil {
+				opts = append(opts, WithLineHandler(tt.args.lineHandler))
+			}
+			if tt.args.metadataHandler != nil {
+				opts = append(opts, WithMetadataHandler(tt.args.metadataHandler))
+			}
+			p := New(tt.args.fields, tt.args.patterns, opts...)
 			if !reflect.DeepEqual(p.Fields, tt.want.parser.Fields) {
 				t.Errorf("got: %v, want: %v", p.Fields, tt.want.parser.Fields)
 			}