------------------------------------------------------------------------------- -- Category class -- This module makes a Category class for use in [[Module:Article history]]. -- It provides a unified interface for the creation of category links. With -- this class, categories can passed between objects without concerns about -- interoperability and still have their values and sort keys easily -- accessible. -------------------------------------------------------------------------------  local checkType = require('libraryUtil').checkType local CATEGORY_NS_TEXT = mw.site.namespaces[14].name  local Category = {} Category.__index = Category  function Category.new(category, sortKey)  checkType('Category.new', 1, category, 'string')  checkType('Category.new', 2, sortKey, 'string', true)  local obj = setmetatable({}, Category)  obj.category = category  obj.sortKey = sortKey  return obj end  function Category:__tostring()  if self.sortKey then  return string.format(  '[[%s:%s|%s]]',  CATEGORY_NS_TEXT,  self.category,  self.sortKey  )  else  return string.format(  '[[%s:%s]]',  CATEGORY_NS_TEXT,  self.category  )  end end  return Category