Programming Groovy 2

19.11 ExpandoMetaClass and DSLs

Categories apply only within the ​use​ blocks, and their effect is fairly limited in scope. If we want the method injection to be effective throughout our application, we can use the ​ExpandoMetaClass​ instead of categories. Let’s use the ​ExpandoMetaClass​ to implement the DSL syntax we saw in the previous section:

Integer.metaClass{
  getDays = { ->
    delegate
  }

  getAgo = { ->
      def date = Calendar.instance
      date.add(Calendar.DAY_OF_MONTH, -delegate)
      date
    }
}

Calendar.metaClass.at = { Map time ->
    def hour = 0
    def minute = 0
    time.each {key, value ->
      hour = key.toInteger()
      minute = value.toInteger()
    }

    delegate.set(Calendar ...