Which of the following functions can be used to declare a class?

To declare a class in Puppet, the include function is used to incorporate the behavior of one class into another. This is particularly important for managing configurations because it allows for the modularization of Puppet code. When you include a class in your Puppet manifest, you are effectively telling Puppet to load and apply the defined settings of that class at the point where it's included, making it a crucial part of organizing and reusing code across different parts of your infrastructure.

The other options do not serve the purpose of declaring a class. For instance, notify is typically used to create notification events within Puppet, allowing for the establishment of dependencies between resources. The compile function pertains to the process of converting Puppet code into a catalog of resources but does not relate directly to class declaration. Assign is not a standard Puppet function for declaring classes or resources, which further distinguishes the role of the include function as the correct choice for that purpose.