Will the C# implementation support proto2 message as well?
What is the compatibility story between proto2 and proto 3? I assume the 
wire format is compatible as long as no proto 3 exclusive features are used.

On Tuesday, August 4, 2015 at 5:43:36 AM UTC-7, Jon Skeet wrote:

> That looks like you're expecting a protobuf.net-style approach - to which 
> the answer is "no" and will continue to be "no".
>
> The C# support will continue to be based on generated code, but there's a 
> new code generator and runtime now in the master branch. The main changes 
> from the previous code are:
>
> - proto3-only support (no proto2 at all)
> - mutable generated types rather than the Java-style builders and 
> immutable messages
>
> Jon
>
> On Monday, 3 August 2015 22:50:06 UTC+1, The Nguyen Xuan wrote:
>>
>> Does this version support object type in C# ?
>>
>> ex:
>>
>> [ProtoMember(1)]
>> public object A {get;set;}
>>
>> thank.
>>
>> Vào 11:51:01 UTC+7 Thứ Năm, ngày 11 tháng 12 năm 2014, Feng Xiao đã viết:
>>>
>>> Hi all,
>>>
>>> I just published protobuf v3.0.0-alpha-1 on our github site:
>>> https://github.com/google/protobuf/releases/tag/v3.0.0-alpha-1
>>>
>>> This is the first alpha release of protobuf v3.0.0. In protobuf v3.0.0, 
>>> we will add a new protobuf language version (aka proto3) and support a 
>>> wider range of programming languages (to name a few: ruby, php, node.js, 
>>> objective-c). This alpha version contains C++ and Java implementation with 
>>> partial proto3 support (see below for details). In future releases we will 
>>> add support for more programming languages and implement the full proto3 
>>> feature set. Besides proto3, this alpha version also includes two other new 
>>> features: map fields and arena allocation. They are implemented for both 
>>> proto3 and the old protobuf language version (aka proto2).
>>>
>>> We are currently working on the documentation of these new features and 
>>> when it's ready it will be updated to our protobuf developer guide 
>>> <https://developers.google.com/protocol-buffers/docs/overview>. For the 
>>> time being if you have any questions regarding proto3 or other new 
>>> features, please post your question in the discussion group.
>>>
>>> CHANGS
>>> =======
>>> Version 3.0.0-alpha-1 (C++/Java):
>>>
>>>   General
>>>   * Introduced Protocol Buffers language version 3 (aka proto3).
>>>
>>>     When protobuf was initially opensourced it implemented Protocol 
>>> Buffers
>>>     language version 2 (aka proto2), which is why the version number
>>>     started from v2.0.0. From v3.0.0, a new language version (proto3) is
>>>     introduced while the old version (proto2) will continue to be 
>>> supported.
>>>
>>>     The main intent of introducing proto3 is to clean up protobuf before
>>>     pushing the language as the foundation of Google's new API platform.
>>>     In proto3, the language is simplified, both for ease of use and  to
>>>     make it available in a wider range of programming languages. At the
>>>     same time a few features are added to better support common idioms
>>>     found in APIs.
>>>
>>>     The following are the main new features in language version 3:
>>>
>>>       1. Removal of field presence logic for primitive value fields, 
>>> removal
>>>          of required fields, and removal of default values. This makes 
>>> proto3
>>>          significantly easier to implement with open struct 
>>> representations,
>>>          as in languages like Android Java, Objective C, or Go.
>>>       2. Removal of unknown fields.
>>>       3. Removal of extensions, which are instead replaced by a new 
>>> standard
>>>          type called Any.
>>>       4. Fix semantics for unknown enum values.
>>>       5. Addition of maps.
>>>       6. Addition of a small set of standard types for representation of 
>>> time,
>>>          dynamic data, etc.
>>>       7. A well-defined encoding in JSON as an alternative to binary 
>>> proto
>>>          encoding.
>>>
>>>     This release (v3.0.0-alpha-1) includes partial proto3 support for 
>>> C++ and
>>>     Java. Items 6 (well-known types) and 7 (JSON format) in the above 
>>> feature
>>>     list are not implemented.
>>>
>>>     A new notion "syntax" is introduced to specify whether a .proto file
>>>     uses proto2 or proto3:
>>>
>>>       // foo.proto
>>>       syntax = "proto3";
>>>       message Bar {...}
>>>
>>>     If omitted, the protocol compiler will generate a warning and 
>>> "proto2" will
>>>     be used as the default. This warning will be turned into an error in 
>>> a
>>>     future release.
>>>
>>>     We recommend that new Protocol Buffers users use proto3. However, we 
>>> do not
>>>     generally recommend that existing users migrate from proto2 from 
>>> proto3 due
>>>     to API incompatibility, and we will continue to support proto2 for a 
>>> long
>>>     time.
>>>
>>>   * Added support for map fields (implemented in C++/Java for both 
>>> proto2 and
>>>     proto3).
>>>
>>>     Map fields can be declared using the following syntax:
>>>
>>>       message Foo {
>>>         map<string, string> values = 1;
>>>       }
>>>
>>>     Data of a map field will be stored in memory as an unordered map and 
>>> it
>>>     can be accessed through generated accessors.
>>>
>>>   C++
>>>   * Added arena allocation support (for both proto2 and proto3).
>>>
>>>     Profiling shows memory allocation and deallocation constitutes a 
>>> significant
>>>     fraction of CPU-time spent in protobuf code and arena allocation is a
>>>     technique introduced to reduce this cost. With arena allocation, new
>>>     objects will be allocated from a large piece of preallocated memory 
>>> and
>>>     deallocation of these objects is almost free. Early adoption shows 
>>> 20% to
>>>     50% improvement in some Google binaries.
>>>
>>>     To enable arena support, add the following option to your .proto 
>>> file:
>>>
>>>       option cc_enable_arenas = true;
>>>
>>>     Protocol compiler will generate additional code to make the generated
>>>     message classes work with arenas. This does not change the existing 
>>> API
>>>     of protobuf messages and does not affect wire format. Your existing 
>>> code
>>>     should continue to work after adding this option. In the future we 
>>> will
>>>     make this option enabled by default.
>>>
>>>     To actually take advantage of arena allocation, you need to use the 
>>> arena
>>>     APIs when creating messages. A quick example of using the arena API:
>>>
>>>       {
>>>         google::protobuf::Arena arena;
>>>         // Allocate a protobuf message in the arena.
>>>         MyMessage* message = Arena::CreateMessage<MyMessage>(&arena);
>>>         // All submessages will be allocated in the same arena.
>>>         if (!message->ParseFromString(data)) {
>>>           // Deal with malformed input data.
>>>         }
>>>         // Must not delete the message here. It will be deleted 
>>> automatically
>>>         // when the arena is destroyed.
>>>       }
>>>
>>>     Currently arena does not work with map fields. Enabling arena in a 
>>> .proto
>>>     file containing map fields will result in compile errors in the 
>>> generated
>>>     code. This will be addressed in a future release.
>>> =======
>>>
>>> Thanks,
>>> Feng
>>>
>>

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