def initialize(params={})
@site = params[:site] or raise ArgumentError,
'Nanoc::OutdatednessChecker#initialize needs a :site parameter'
@checksum_store = params[:checksum_store] or raise ArgumentError,
'Nanoc::OutdatednessChecker#initialize needs a :checksum_store parameter'
@dependency_tracker = params[:dependency_tracker] or raise ArgumentError,
'Nanoc::OutdatednessChecker#initialize needs a :dependency_tracker parameter'
@basic_outdatedness_reasons = {}
@outdatedness_reasons = {}
@objects_outdated_due_to_dependencies = {}
end