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August 30, 2009

Groovy Goodness: The Spread-Dot Operator

Groovy adds some nice operators to the language to write brief code. We already learned about the Elvis operator and the Spaceship operator. And now we see what the spread-dot operator is about and what it does.

The spread-dot operator (*.) is used to invoke a method on all members of a Collection object. The result of using the spread-dot operator is another Collection object. Here is some sample code:

class Language {
    String lang
    def speak() { "$lang speaks." }

// Create a list with 3 objects. Each object has a lang 
// property and a speak() method. 
def list = [     
    new Language(lang: 'Groovy'),     
    new Language(lang: 'Java'),     
    new Language(lang: 'Scala') 

// Use the spread-dot operator to invoke the speak() method. 
assert ['Groovy speaks.', 'Java speaks.', 'Scala speaks.'] == list*.speak() 
assert ['Groovy speaks.', 'Java speaks.', 'Scala speaks.'] == list.collect{ it.speak() }  

// We can also use the spread-dot operator to access 
// properties, but we don't need to, because Groovy allows 
// direct property access on list members. 
assert ['Groovy', 'Java', 'Scala'] == list*.lang 
assert ['Groovy', 'Java', 'Scala'] == list.lang