CSC/ECE 517 Fall 2009/wiki2 1 SA

Metaprogramming

Introduction

Metaprogramming,is the creation of procedures and programs that automatically construct the definitions of other procedures and programs. Metaprogramming automates some of the tedious and error-prone parts of the programmer's job.

Metaprogramming in various languages

There are many languages that do metaprogramming. Metaprogramming in Groovy Below example demonstrates using classes from the Jakarta Commons Lang package for metaprogramming. All of the methods in org.apache.commons.lang.StringUtils coincidentally follow the Category pattern — static methods that accept a String as the first parameter. This means that you can use the StringUtils class right out of the box as a Category.

import org.apache.commons.lang.StringUtils

class CommonsTest extends GroovyTestCase{
  void testStringUtils(){
    def word = "Introduction"

    word.metaClass.whisper = {->
      delegate.toLowerCase()
    }

    use(StringUtils, StringHelper){
      //from org.apache.commons.lang.StringUtils
      assertEquals "Intro...", word.abbreviate(8)

      //from the StringHelper Category
      assertEquals "INTRODUCTION", word.shout()

      //from the word.metaClass
      assertEquals "introduction", word.whisper()
    }
  } 
}

class StringHelper{
  static String shout(String self){
    return self.toUpperCase()
  }
}