Issue #5517 has been updated by Josh Cooper.

Andrew Forgue wrote:
> Nick Lewis wrote:
> > Given that we eagerly evaluate parameterized classes, I can't conceive of a 
> > model of evaluation that could cause this to work correctly. Essentially 
> > the first thing we end up evaluating is class a, at which point we 
> > immediately execute the notices, because they're functions. Changing the 
> > notices to notify resources can reconcile this behavior in the presence of 
> > futures, should we ever choose to implement those. But for notices, I can't 
> > see a way this could ever work reasonably.
> 
> Why are parameterized classes eagerly evaluated?

To fix this https://projects.puppetlabs.com/issues/4778. 

'include' causes the contents of the class to be evaluated immediately, but 
evaluation of 'class { foo: }' was being deferred. The fix for #4778 changed 
the latter to be eagerly evaluated (to be consistent with the former), but in 
doing so broke the ability to override included parameterized classes. 
----------------------------------------
Bug #5517: behavior change within 2.6 makes it impossible to override class 
parameters of "included" parametrized classes
https://projects.puppetlabs.com/issues/5517

Author: Peter Meier
Status: Accepted
Priority: High
Assignee: Nick Lewis
Category: language
Target version: 2.6.x
Affected Puppet version: 2.6.3
Keywords: parameterized_classes
Branch: 


In 2.6.1 the following recipe:

<pre>
class a(
  $b_c = { 'b' => 'foo' }
) {
  notice $a::b_c
  if $a::b_c {
    notice $a::b_c['b']
  }
}

class b {
  class{'a': b_c => false }
}

class b::c inherits b {
  Class['a']{ b_c => { 'b' => 'bleh' } }
}

class b::d {
  include ::b::c
}

include b::d
</pre>

produces the following output:

<pre>
$ puppet foo.pp 
notice: Scope(Class[A]): bbleh
notice: Scope(Class[A]): bleh
</pre>

Which is what I expected. However with 2.6.3 it produces the following output:

<pre>
# puppet foo.pp 
notice: Scope(Class[A]): false
</pre>

Imho likely the changes for #4778 and #5074 are responsible for that behavior 
change.

However this makes it impossible to overwrite parameters of a "included" 
parametrized class in a subclass. There are only ugly workarounds for that 
problem and I think this should actually work as it did within 2.6.1. Otherwise 
the usefulness of parametrized classes is quite reduced.


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