Need help understanding Groovy Lists

Question

I am new to the Groovy language. Can someone please explain to me what this line of code means?

List<String> somevar = [].withDefault { }

Thanks.

Answer 1

As it says in the documentation :

Decorates a list allowing it to grow when called with a non-existent index value. When called with such values, the list is grown in size and a default value is placed in the list by calling a supplied init Closure

There's a good blog post about it here

Answer 2

It gives a default value for elements not yet in the list. For example

List<String> somevar = [].withDefault { }
println "Value at index 0 is "+somevar[0]; // gives null
println "Value at index 5 is "+somevar[5]; // gives null

List<String> somevarb = ['a'].withDefault { 'b' };
println "Value at index 0 is "+somevarb[0]; // gives a
println "Value at index 5  is "+somevarb[5]; // gives b

So when its empty like in your case it gives null . Read more here