On 28 January 2016 at 23:01, Adam Stokes <adam.sto...@canonical.com> wrote: > Why would someone want to use this instead of what's provided in > charmhelpers?
This wraps what is provided in charmhelpers. To use raw charmhelpers, you need to write the hooks and handlers to call its features at the right time and in the right order. You need to call fetch.configure_sources, whenever the relevant config items change. You need to install the list of extra packages, whenever the relevant config item changes. You need to repin held packages, if the option is set, whenever new packages are installed. To use the layer, you just add an entry to layers.yaml and get it all done for you, and it is all done consistently across all charms using the layer. You don't have to worry about inconsistencies between your reimplementation of the wheel with the next charms reimplementation of the wheel causing confusion to users. It also removes all the boilerplate. You don't need to include all that gumph in your config.yaml. It sets reactive states your handlers can wait on so you don't have to set reactive states your handlers can wait on. By requesting a package install and having handlers wait on the install to complete, you get to write highly decoupled code without losing efficiency. Several different handlers in different parts of the code base and even in different layers can all schedule the packages they care about to be installed, and have a single apt-get update run, and only if necessary. Improvements to the layer improve all charms using the layer. When Juju charm configuration gets richer data structures, we can write all the migration, compatibility and deprecation stuff once and all charms get it next time they are built. Fixes in the charmhelpers codebase can't fix its callsites or improve the documentation in your config.yaml. So you want to use it to save initial work and future maintenance :) -- Stuart Bishop <stuart.bis...@canonical.com> -- Juju mailing list Juju@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/juju
