2013-09-04-capnproto-0.3-python-tools-features.md (5702B)
1 --- 2 layout: post 3 title: "Cap'n Proto v0.3: Python, tools, new features" 4 author: kentonv 5 --- 6 7 The first release of Cap'n Proto came three months after the project was announced. The second 8 release came six weeks after that. And the third release is three weeks later. If the pattern 9 holds, there will be an infinite number of releases before the end of this month. 10 11 Version 0.3 is not a paradigm-shifting release, but rather a slew of new features largely made 12 possible by building on the rewritten compiler from the last release. Let's go through the 13 list... 14 15 ### Python Support! 16 17 Thanks to the tireless efforts of contributor [Jason Paryani](https://github.com/jparyani), I can 18 now comfortably claim that Cap'n Proto supports multiple languages. [His Python 19 implementation](http://jparyani.github.io/pycapnp/) wraps the C++ library and exposes 20 most of its features in a nice, easy-to-use way. 21 22 And I have to say, it's _way_ better than the old Python Protobuf implementation that I helped put 23 together at Google. Here's why: 24 25 * Jason's implementation parses Cap'n Proto schema files at runtime. There is no need to run a 26 compiler to generate code every time you update your schema, as with protobufs. So, you get 27 to use Python the way Python was intended to be used. In fact, he's hooked into the Python 28 import mechanism, so you can basically import a `.capnp` schema file as if it were a `.py` 29 module. It's even convenient to load schema files and play with Cap'n Proto messages from the 30 interactive interpreter prompt. 31 * It's _fast_. Whereas the Python Protobuf implementation -- which we made the mistake of 32 implementing in pure-Python -- is _slow_. And while technically there is an experimental 33 C-extension-based Python Protobuf implementation (which isn't enabled by default due to various 34 obscure problems), Jason's Cap'n Proto implementation is faster than that, too. 35 36 Go [check it out](http://jparyani.github.io/pycapnp/)! 37 38 By the way, there is also a budding [Erlang implementation](http://ecapnp.astekk.se/) 39 (by Andreas Stenius), and work 40 continues on [Rust](https://github.com/dwrensha/capnproto-rust) (David Renshaw) and 41 [Ruby](https://github.com/cstrahan/capnp-ruby) (Charles Strahan) implementations. 42 43 ### Tools: Cap'n Proto on the Command Line 44 45 The `capnp` command-line tool previously served mostly to generate code, via the `capnp compile` 46 command. It now additionally supports converting encoded Cap'n Proto messages to a human-readable 47 text format via `capnp decode`, and converting that format back to binary with `capnp encode`. 48 These tools are, of course, critical for debugging. 49 50 You can also use the new `capnp eval` command to do something interesting: given a schema file and 51 the name of a constant defined therein, it will print out the value of that constant, or optionally 52 encode it to binary. This is more interesting than it sounds because the schema language supports 53 variable substitution in the definitions of these constants. This means you can build a large 54 structure by importing smaller bits from many different files. This may make it convenient to 55 use Cap'n Proto schemas as a config format: define your service configuration as a constant in 56 a schema file, importing bits specific to each client from other files that those clients submit 57 to you. Use `capnp eval` to "compile" the whole thing to binary for deployment. (This has always 58 been a common use case for Protobuf text format, which doesn't even support variable substitution 59 or imports.) 60 61 Anyway, check out the [full documentation]({{ site.baseurl }}capnp-tool.html) for 62 more. 63 64 ### New Features 65 66 The core product has been updated as well: 67 68 * Support for unnamed [unions]({{ site.baseurl }}language.html#unions) reduces the 69 need for noise-words, improving code readability. Additionally, the syntax for unions has been 70 simplified by removing the unnecessary ordinal number. 71 * [Groups]({{ site.baseurl }}language.html#groups) pair nicely with unions. 72 * [Constants]({{ site.baseurl }}language.html#constants) are now 73 [implemented in C++]({{ site.baseurl }}cxx.html#constants). Additionally, they 74 can now be defined in terms of other constants (variable substitution), as described earlier. 75 * The schema API and `schema.capnp` have been radically refactored, in particular to take advantage 76 of the new union and group features, making the code more readable. 77 * More and better tests, bug fixes, etc. 78 79 ### Users! 80 81 Some news originating outside of the project itself: 82 83 * [Debian Unstable (sid)](http://www.debian.org/releases/sid/) now features 84 [a Cap'n Proto package](http://packages.debian.org/sid/capnproto), thanks to 85 [Tom Lee](https://github.com/thomaslee). Of course, since package updates take some time, this 86 package is still v0.2.1 as of this writing, but it will be updated to v0.3 soon enough. 87 * Popular OSX-based text editor [TextMate](http://macromates.com/) now 88 [uses Cap'n Proto internally](https://github.com/textmate/textmate/commit/5c02b4ff5cc0c7c319d3d4f127c8ee19b81f80b7), 89 and the developer's feedback lead directly to several usability improvements included in this 90 release. 91 * Many people using Cap'n Proto _haven't bothered to tell us about it_! Please, if you use it, 92 [let us know](https://groups.google.com/group/capnproto) about your experience, both what you like 93 and especially what you don't like. This is the critical time where the system is usable but 94 can still be changed if it's not right, so your feedback is critical to our long-term success. 95 * I have revenue! A whopping [$1.25 per week](https://www.gittip.com/kentonv/)! >_> It's 96 totally worth it; I love this project. (But thanks for the tips!)