Google Protobuf: proto3 enhancements

Proto3 is the new version of Google Protobuf with various enhancements and additions. Let's go over them one by one.

1. Since all fields are optional by default. Hence "optional" keyword has been done away with. If nothing is specified, it will be considered optional. (Protof files just became a tad smaller)

	//proto2
	optional string phone = 3;
	//proto3
	string phone = 3;

view raw proto2proto2.proto hosted with ❤ by GitHub

2. Support to group fields are not longer there. Group was just another way of nesting information in messages. But it was inefficient way to do (better way, Nested Messages). Hence is no longer supported.

	//Group Message, Not allowed in proto3
	message SchoolRecord {
	repeated group SudentRecord = 1 {
	required string roll_no = 2;
	optional string name = 3;
	}
	}
	//Nested Message Format, allowed both in proto2 and proto3
	message SchoolRecord {
	message SudentRecord {
	required string roll_no = 1;
	optional string name = 2;
	}
	repeated SudentRecord student_record = 1;
	}

view raw group.proto hosted with ❤ by GitHub

3. Packed repeated fields were introduced in 2.1.0. Repeated fields needed to be explicitly set packed=true to use this encoding. In proto3, repeated primitive fields have been made packed by default. They have to be set false to be disabled. 

	//proto2
	message Student {
	repeated int32 roll_no= 1 [packed=true];
	}
	//proto 3
	message Student {
	repeated int32 roll_no= 1;
	}

view raw packed.proto hosted with ❤ by GitHub

4. Common proto types (timestamp.proto etc) have been added. They can be used after importing. This takes a step towards usable library in protobuf. See below,

	syntax = "proto3";
	package google.protobuf;
	option java_generate_equals_and_hash = true;
	option java_multiple_files = true;
	option java_outer_classname = "TimestampProto";
	option java_package = "com.google.protobuf";
	option csharp_namespace = "Google.ProtocolBuffers";
	option objc_class_prefix = "GPB";
	message Timestamp {
	int64 seconds = 1;
	int32 nanos = 2;
	}

view raw timestamp.proto hosted with ❤ by GitHub

5. reserverd keyword introduced. By this, user has the control over reserved field_names and field_numbers. Once declared as reserved, these can't be used anywhere in the message.

Below, the field_numbers and names can't be used anywhere in the message again. Gives us more control.

	//field_numbers
	message Student {
	reserved 401, 501, 601 to 604, 701;
	}
	//field_names
	message Student {
	reserved "monitor", "teacher";
	}

view raw reserved.proto hosted with ❤ by GitHub

6. Support for Objective-C and C# introduced in proto3. yay!

7. There are other language specific changes for various languages.