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

The function that is used to declare a class within Puppet manifests is the 'include' function. When you declare a class in Puppet, you do so by using the include keyword followed by the class name. This keyword is fundamental in Puppet for incorporating the defined behavior and configurations of that class into the catalog, which specifies what resources should be managed and how they should be configured.

Using 'include,' you integrate a class into another class or manifest, allowing Puppet to apply the resources defined within the included class. This modular approach promotes code reuse and organization in configuration management.

The other options, such as notify, compile, and assign, serve different purposes in Puppet. Notify is used for setting up notifications for resources to trigger other actions; compile refers to the process of assembling the Puppet resources into a catalog for execution, and assign does not apply to class declaration but could imply setting values or parameters in certain contexts. Each plays a distinct role, but none serve the specific function of declaring a class in a Puppet manifest.