A new release of system is now available!
https://github.com/danielsz/system
[org.danielsz/system "0.4.0"]
This release represents a milestone, hence the major version bump. It
is breaking only with regards to the Duct-style components. This is
also where most of the innovation took place.
The Duct components, an idea that originated with James Reeves,
revolves around a handler, endpoints and middleware. Compojure gave us
means to route http requests, Duct builds on that work and allows us
to group routes by purpose, exposing them to the dependencies they
need.
The endpoints are in fact closures on top of routes with the
dependencies available in lexical scope. So are middleware components
(at this point, this is true only for system’s implementation of
Duct).
The original Duct mini-framework boasts a data-driven configuration. At
system, we provide a code-driven configuration that maps nicely with
the way classical (Stuart Sierra) components are configured.
A minimal system would look like that:
(component/system-map
:db (new-database)
:endpoint (component/using (new-endpoint ring-handler) [:db])
:middleware (new-middleware {:middleware [[[wrap-not-found]]]})
:handler (component/using (new-handler) [:endpoint :middleware])
Middleware can be applied globally and/or on a per endpoint
basis. This addresses real-world scenarios where some endpoints may
need different middleware than other endpoints. An example of this is
the Sente routes that don’t tolerate data format middleware as it does
its own serialization.
Duct components allow web developers to write specialized endpoints in
isolation and (re)use them in application code with ease. For example,
a social sign-in library that has endpoints for the Facebook login
workflow, can be (re)used like so:
(component/system-map
:db (new-database)
:app-endpoint (component/using (new-endpoint ring-handler) [:db])
:facebook-endpoint (new-endpoint facebook)
:middleware (new-middleware {:middleware [[[wrap-not-found]]]})
:handler (component/using (new-handler) [:app-endpoint :facebook-endpoint
:middleware])
And voilà, your web app now does Facebook sign in.
If you haven’t looked at system yet, here are a couple of reasons why
you should.
- system brings very little semantics of its own (a good thing in my
book!), it embraces the coding discipline and philosophy of its
constituent parts: Component, Boot, Duct, etc.
- system is stable and battle-tested (running in production for
several years already).
- system has excellent live coding facilities. It even offers a Lisp
mode where the REPL behaves the same way it does in all Lisp
systems: redefine away until it breaks.
On the other hand, documentation is sparse. Efforts are under way to
remedy the situation. Docstrings adorn the Duct namespaces thanks to a
recent PR by Arne Brasseur. I have plans to build a project homepage
with educational material. Blog posts and/or screencasts will be very
much appreciated.
The complete changelog:
https://github.com/danielsz/system/blob/master/CHANGELOG.org#040
This release was made possible with the contributions of:
Arne Brasseur
Wei Hsu
Alex Miller
Andreas Rottmann
John Swanson
Thank you so much!
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