finalize

If a class defines a finalize method, when an instance of that class is
garbage-collected that method will be invoked:

class Foo
  def finalize
    # Invoked when Foo is garbage-collected
    # Use to release non-managed resources (ie. C libraries, structs)
  end
end

Use this method to release resources allocated by external libraries that are
not directly managed by Crystal garbage collector.

Examples of this can be found in IO::FileDescriptor#finalize
or OpenSSL::Digest#finalize.

Notes:

• The finalize method will only be invoked once the object has been
  fully initialized via the initialize method. If an exception is raised
  inside the initialize method, finalize won’t be invoked. If your class
  defines a finalize method, be sure to catch any exceptions that might be
  raised in the initialize methods and free resources.

• Allocating any new object instances during garbage-collection might result
  in undefined behavior and most likely crashing your program.