Exploring macro hooks
Macro hooks are special macro definitions that are invoked by the Crystal compiler in some situations at compile time. These include the following:
inheritedis invoked when a subclass is defined, where@typeis the inheriting type.includedis invoked when a module is included, where@typeis the including type.extendedis invoked when a module is extended, where@typeis the extending type.method_missingis invoked when a method is not found and is passed a singleCallargument.method_addedis invoked when a new method is defined in the current scope and is passed a singleDefargument.finishedis invoked after the semantic analysis phase, so all the types and their methods are known.
The first three and finished definitions are the most common/useful ones, so we are going to focus on those here. The first three hooks all work essentially the same – they just execute in different contexts. For example, the following...