add NoopVisitor

README.md

@@ -39,9 +39,21 @@ Package in Go for parsing Google Protocol Buffers [.proto files version 2 + 3](h
 	}
 
 	func handleMessage(m *proto.Message) {
+		lister := new(optionLister)
+		for _, each := range m.Elements {
+			each.Accept(lister)
+		}
 		fmt.Println(m.Name)
 	}
 
+	type optionLister struct {
+		proto.NoopVisitor
+	}
+
+	func (l optionLister) VisitOption(o *proto.Option) {
+		fmt.Println(o.Name)
+	}
+
 ### validation
 
 Current parser implementation is not completely validating `.proto` definitions.
@@ -53,4 +65,4 @@ Use some linting tools (e.g. https://github.com/uber/prototool) or `protoc` for
 See [proto-contrib](https://github.com/emicklei/proto-contrib) for other contributions on top of this package such as protofmt, proto2xsd and proto2gql.
 [protobuf2map](https://github.com/emicklei/protobuf2map) is a small package for inspecting serialized protobuf messages using its `.proto` definition.
 
-© 2017, [ernestmicklei.com](http://ernestmicklei.com).  MIT License. Contributions welcome.
+© 2017-2022, [ernestmicklei.com](http://ernestmicklei.com).  MIT License. Contributions welcome.

noop_visitor.go

@@ -0,0 +1,48 @@
+// Copyright (c) 2022 Ernest Micklei
+//
+// MIT License
+//
+// Permission is hereby granted, free of charge, to any person obtaining
+// a copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to
+// permit persons to whom the Software is furnished to do so, subject to
+// the following conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+package proto
+
+// NoopVisitor is a no-operation visitor that can be used when creating your own visitor that is interested in only one or a few types.
+// It implements the Visitor interface.
+type NoopVisitor struct{}
+
+func (n NoopVisitor) VisitMessage(m *Message)         {}
+func (n NoopVisitor) VisitService(v *Service)         {}
+func (n NoopVisitor) VisitSyntax(s *Syntax)           {}
+func (n NoopVisitor) VisitPackage(p *Package)         {}
+func (n NoopVisitor) VisitOption(o *Option)           {}
+func (n NoopVisitor) VisitImport(i *Import)           {}
+func (n NoopVisitor) VisitNormalField(i *NormalField) {}
+func (n NoopVisitor) VisitEnumField(i *EnumField)     {}
+func (n NoopVisitor) VisitEnum(e *Enum)               {}
+func (n NoopVisitor) VisitComment(e *Comment)         {}
+func (n NoopVisitor) VisitOneof(o *Oneof)             {}
+func (n NoopVisitor) VisitOneofField(o *OneOfField)   {}
+func (n NoopVisitor) VisitReserved(r *Reserved)       {}
+func (n NoopVisitor) VisitRPC(r *RPC)                 {}
+func (n NoopVisitor) VisitMapField(f *MapField)       {}
+
+// proto2
+func (n NoopVisitor) VisitGroup(g *Group)           {}
+func (n NoopVisitor) VisitExtensions(e *Extensions) {}