find_extension

Examines source and its ancestors and returns the "deepest" Source having an SourceExtension with the given extension_name .

If neither source nor any of its ancestors have such an extension, the function returns null.

This function is useful in cases when an SourceExtension is meant to apply to both the Source it belongs to and the Source's descendants.

A common example is the SourceCollection extension, where descendants of an Source having an SourceCollection extension are implied to be members of that collection. In that example, this function can be used to test whether source is a member of a collection.

The returned Source is referenced for thread-safety and must be unreferenced with unref when finished with it.

Note the function returns the Source containing the SourceExtension instead of the SourceExtension itself because extension instances are not to be referenced directly (see get_extension).

Parameters:

this	an SourceRegistry
source	an Source
extension_name	the extension name to find

Returns:

an Source, or null if no match was found