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Add Cap'n Proto source

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+---
+layout: post
+title: "Cap'n Proto v0.3: Python, tools, new features"
+author: kentonv
+---
+
+The first release of Cap'n Proto came three months after the project was announced.  The second
+release came six weeks after that.  And the third release is three weeks later.  If the pattern
+holds, there will be an infinite number of releases before the end of this month.
+
+Version 0.3 is not a paradigm-shifting release, but rather a slew of new features largely made
+possible by building on the rewritten compiler from the last release.  Let's go through the
+list...
+
+### Python Support!
+
+Thanks to the tireless efforts of contributor [Jason Paryani](https://github.com/jparyani), I can
+now comfortably claim that Cap'n Proto supports multiple languages.  [His Python
+implementation](http://jparyani.github.io/pycapnp/) wraps the C++ library and exposes
+most of its features in a nice, easy-to-use way.
+
+And I have to say, it's _way_ better than the old Python Protobuf implementation that I helped put
+together at Google.  Here's why:
+
+* Jason's implementation parses Cap'n Proto schema files at runtime.  There is no need to run a
+  compiler to generate code every time you update your schema, as with protobufs.  So, you get
+  to use Python the way Python was intended to be used.  In fact, he's hooked into the Python
+  import mechanism, so you can basically import a `.capnp` schema file as if it were a `.py`
+  module.  It's even convenient to load schema files and play with Cap'n Proto messages from the
+  interactive interpreter prompt.
+* It's _fast_.  Whereas the Python Protobuf implementation -- which we made the mistake of
+  implementing in pure-Python -- is _slow_.  And while technically there is an experimental
+  C-extension-based Python Protobuf implementation (which isn't enabled by default due to various
+  obscure problems), Jason's Cap'n Proto implementation is faster than that, too.
+
+Go [check it out](http://jparyani.github.io/pycapnp/)!
+
+By the way, there is also a budding [Erlang implementation](http://ecapnp.astekk.se/)
+(by Andreas Stenius), and work
+continues on [Rust](https://github.com/dwrensha/capnproto-rust) (David Renshaw) and
+[Ruby](https://github.com/cstrahan/capnp-ruby) (Charles Strahan) implementations.
+
+### Tools: Cap'n Proto on the Command Line
+
+The `capnp` command-line tool previously served mostly to generate code, via the `capnp compile`
+command.  It now additionally supports converting encoded Cap'n Proto messages to a human-readable
+text format via `capnp decode`, and converting that format back to binary with `capnp encode`.
+These tools are, of course, critical for debugging.
+
+You can also use the new `capnp eval` command to do something interesting: given a schema file and
+the name of a constant defined therein, it will print out the value of that constant, or optionally
+encode it to binary.  This is more interesting than it sounds because the schema language supports
+variable substitution in the definitions of these constants.  This means you can build a large
+structure by importing smaller bits from many different files.  This may make it convenient to
+use Cap'n Proto schemas as a config format: define your service configuration as a constant in
+a schema file, importing bits specific to each client from other files that those clients submit
+to you.  Use `capnp eval` to "compile" the whole thing to binary for deployment.  (This has always
+been a common use case for Protobuf text format, which doesn't even support variable substitution
+or imports.)
+
+Anyway, check out the [full documentation]({{ site.baseurl }}capnp-tool.html) for
+more.
+
+### New Features
+
+The core product has been updated as well:
+
+* Support for unnamed [unions]({{ site.baseurl }}language.html#unions) reduces the
+  need for noise-words, improving code readability.  Additionally, the syntax for unions has been
+  simplified by removing the unnecessary ordinal number.
+* [Groups]({{ site.baseurl }}language.html#groups) pair nicely with unions.
+* [Constants]({{ site.baseurl }}language.html#constants) are now
+  [implemented in C++]({{ site.baseurl }}cxx.html#constants).  Additionally, they
+  can now be defined in terms of other constants (variable substitution), as described earlier.
+* The schema API and `schema.capnp` have been radically refactored, in particular to take advantage
+  of the new union and group features, making the code more readable.
+* More and better tests, bug fixes, etc.
+
+### Users!
+
+Some news originating outside of the project itself:
+
+* [Debian Unstable (sid)](http://www.debian.org/releases/sid/) now features
+  [a Cap'n Proto package](http://packages.debian.org/sid/capnproto), thanks to
+  [Tom Lee](https://github.com/thomaslee).  Of course, since package updates take some time, this
+  package is still v0.2.1 as of this writing, but it will be updated to v0.3 soon enough.
+* Popular OSX-based text editor [TextMate](http://macromates.com/) now
+  [uses Cap'n Proto internally](https://github.com/textmate/textmate/commit/5c02b4ff5cc0c7c319d3d4f127c8ee19b81f80b7),
+  and the developer's feedback lead directly to several usability improvements included in this
+  release.
+* Many people using Cap'n Proto _haven't bothered to tell us about it_!  Please, if you use it,
+  [let us know](https://groups.google.com/group/capnproto) about your experience, both what you like
+  and especially what you don't like.  This is the critical time where the system is usable but
+  can still be changed if it's not right, so your feedback is critical to our long-term success.
+* I have revenue!  A whopping [$1.25 per week](https://www.gittip.com/kentonv/)!  >_>  It's
+  totally worth it; I love this project.  (But thanks for the tips!)