Puppet users - May 2011 - Inheritance in parametrized classes

Hi,

I''m trying to pass a parameter different from the default to the child 
of a parametrized class with inheritance, but the inherited code from 
the parent class doesn''t seem to be taking the correct parameter.

For example, in the following code:


class parent ( $foo = "bar" ) {
     notice("parent: foo is $foo ")
}

class child ( $foo = "bar" ) inherits parent {
     notice("child: foo is $foo ")
}

class { "child": foo => "test" }


I would expect the following result:

notice: Scope(Class[Parent]): parent: foo is test
notice: Scope(Class[Child]): child: foo is test

I''m getting the following one instead:

notice: Scope(Class[Parent]): parent: foo is bar
notice: Scope(Class[Child]): child: foo is test

Is that the correct behaviour?

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On May 20, 10:20 am, Carles Amigó <carles.am...@softonic.com>
wrote:
> Hi,
>
> I''m trying to pass a parameter different from the default to the
child
> of a parametrized class with inheritance,

I would not recommend mixing class inheritance with parameterized
classes.

As a separate matter, I would recommend to most people to avoid
parameterized classes altogether.

> but the inherited code from
> the parent class doesn''t seem to be taking the correct parameter.
>
> For example, in the following code:
>
> class parent ( $foo = "bar" ) {
>      notice("parent: foo is $foo ")
>
> }
>
> class child ( $foo = "bar" ) inherits parent {
>      notice("child: foo is $foo ")
>
> }
>
> class { "child": foo => "test" }
>
> I would expect the following result:
>
> notice: Scope(Class[Parent]): parent: foo is test
> notice: Scope(Class[Child]): child: foo is test
>
> I''m getting the following one instead:
>
> notice: Scope(Class[Parent]): parent: foo is bar
> notice: Scope(Class[Child]): child: foo is test
>
> Is that the correct behaviour?

"Correct" is such a nuanced word.  I don''t know whether the
observed
behavior is by design, but I don''t find it surprising.  I would not
have found your expected behavior surprising either, however.

You may be able to achieve your desired result like this:

class { "parent": foo => "test" }
class { "child": foo => "test" }


That is, it is safe to include both a class and one of its subclasses
in the same manifest.  Do be aware, however, that you should create
subclasses *only* to override superclass resource properties.  And
with parameterized classes, you can achieve an equivalent result via
class parameters instead.

If you want a class that declares all the resources of another, plus
more, then have one class "include" the other instead of inheriting
it.  Except don''t do that with parameterized classes: Puppet Labs
recommends against it, and there are practical reasons to avoid doing
so.


John

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> "Correct" is such a nuanced word.  I don''t know whether
the observed
> behavior is by design, but I don''t find it surprising.  I would
not
> have found your expected behavior surprising either, however.
>
> You may be able to achieve your desired result like this:
>
> class { "parent": foo =>  "test" }
> class { "child": foo =>  "test" }
Yes, I finally reached the same conclusion. This is exactly how I fixed it.
> That is, it is safe to include both a class and one of its subclasses
> in the same manifest.  Do be aware, however, that you should create
> subclasses *only* to override superclass resource properties.  And
> with parameterized classes, you can achieve an equivalent result via
> class parameters instead.
In this example I wasn''t overriding any property but I was doing so in 
my "real" case, so inheritance was needed here.
> If you want a class that declares all the resources of another, plus
> more, then have one class "include" the other instead of
inheriting
> it.  Except don''t do that with parameterized classes: Puppet Labs
> recommends against it, and there are practical reasons to avoid doing
> so.
That''s how I''m doing it when I don''t have to override
any property. IMHO
It''s becoming more and more difficult to know what''s the
correct way to
do something since the introduction of the parametrized classes. They 
are a huge improvement though.

Cheers

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