On Tue, Mar 18, 2014 at 9:31 PM, Sage Imel <[email protected]> wrote:
> With the future parser enabling selectors to used in the case of another
> selector it's possible to use selectors to specialize on multiple facts or
> other values very concisely.
>
>
Sage, thanks for trying out the future parser and giving us feedback.
> $puppet_conf_file_path = $::osfamily ? {
> 'Debian' => $::operatingsystem ? {
> 'Ubuntu' => '/pretending/ubuntu/is/special/here'/puppet/puppet.conf',
> default =>
> '/pretending/debian/in/general/is/special/in/a/different/way/here/puppet/puppet.conf',
> default => '/etc/puppet/puppet.conf'
> }
>
> But sometimes setting a default value is not the desired behavior for
> unmatched cases. Sometimes, like in a params class, you'd rather just fail
> the whole puppet run when an unmatched case is hit.
>
> class puppet::params(
> # In this case we are only specializing based on one parameter
> $conf_file_path = $::osfamily ? {
> 'Debian' => '/etc/puppet/puppet.conf',
> default => fail("osfamily ${::osfamily} is not supported by this
> module"),
> },
> #in this case we are specializing based on multiple parameters
> $vardir = $::osfamily ? {
> 'Debian' => $operatingsystem ? {
> 'Debian' => '/var/lib/puppet',
> default => fail("operatingsystem ${::operatingsystem} is not
> supported by this module"),
> },
> default => fail("osfamily ${::osfamily} is not supported by this
> module"),
> },
> ){}
>
>
You are right, this doesn't work in 3.4.3. If you try out 3.5.0-rc1 we've
starting implementing a new language evaluator that can do this. Here is an
example:
> cat t.pp
$x = $kernel ? { default => fail("no!") }
[09:21:23][Ruby(ruby-1.8.7-p374)][Git(stable)] andy:puppet
> be puppet apply t.pp --parser future
Error: no! on node aparker.corp.puppetlabs.net
Error: no! on node aparker.corp.puppetlabs.net
> This almost works with the future parser. Except that puppet errors out on
> the cases that hit the fail call because the fail function doesn't return
> an rvalue.
>
> Making it possible to use fail in selectors would make this pattern very
> versatile and could greatly simplify params classes. You can set the
> parameters in all valid cases and throw errors with messages that are
> tailored to the exact context without having to repeat logic or variable
> names. This pattern also lets you see for sure at a glance that a parameter
> is being set (or that the run will fail) which is harder to see when doing
> the same thing with conds since you have to examine all the case blocks.
>
> The easier way to make this work would probably be to make fail return a
> value (maybe the error message that would be shown). But it doesn't make
> sense to me that fail should check if it's expected to yield an rvalue
> since fail completely changes the flow of execution and will would never
> make it to returning a value anyways, so making the change there makes more
> sense to me.
>
We are removing the rvalue vs. statement distinction for functions in the
future parser/evaluator work and the distinction will be gone in puppet 4.
Having the distinction did little more than cause confusion and
frustration, as you just experienced.
>
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--
Andrew Parker
[email protected]
Freenode: zaphod42
Twitter: @aparker42
Software Developer
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