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Saturday, October 3, 2009

Groovy Goodness: Mixin Functionality to Classes

In a previous blog post we learned how to use Categories to add functionality to existing class. We had to use the use keyword to define a block in which the Category was valid. But we can also add new functionality with the @Mixin compile-time annotation or at runtime with the mixin() method (GDK extension to Class).

class Pirate {
    def talk(text) {
        "Aargh, walk the plank. ${text}"
    }
}

// Compile time mixin to Talk class. This add all
// methods from Pirate to Talk.
@Mixin(Pirate)  
class Talk {}

assert 'Aargh, walk the plank. Give me a bottle of rum.' == new Talk().talk("Give me a bottle of rum.")
import org.apache.commons.lang.StringUtils

class Parrot {
    static String speak(String text) {
        /Parrot says "$text"/
    }
}

// Runtime mixin on String class. 
// mixin() is a GDK extension to Class.
String.mixin Parrot, StringUtils

assert 'Parrot says "mrhaki"' == 'mrhaki'.speak()
assert 'Groovy is so much...' == 'Groovy is so much fun.'.abbreviate(20)  // StringUtils mixin.