Passing parameters to classes

Sometimes it's very useful to parameterize some aspect of a class. For example, you might need to manage different versions of a gem package, and rather than making separate classes for each which differ only in the version number, or using inheritance and overrides, you can pass in the version number as a parameter.

How to do it…

In this example we'll create a definition which accepts parameters:

1. Declare the parameter as a part of the class definition:

   class eventmachine($version) {
     package { 'eventmachine':
       provider => gem,
       ensure   => $version,
     }
   }

2. Use the following syntax to include the class on a node:

   class { 'eventmachine':
     version => '1.0.3',
   }

How it works…

The class definition

class eventmachine($version) {

is just like a normal class definition except it specifies that the class takes one parameter: $version. Inside the class, we've defined a package resource:

package { 'eventmachine':
  provider => gem,
  ensure   => $version,
...