Question

The following code will produce an assertion error

def foo(a,b,c='awesome',d=null) {
    assert d
}

foo(1,2,d='bar')

Why does it give an error? Why is the keyword assignment of d not working? I find this very different from Python keyword argument.

Answer 1

Groovy doesn’t do keyword arguments quite the same as python.

First, the syntax is map-like. Instead of

foo(1,2,d='bar')

you need

foo(1,2,d:'bar')

Second, groovy can’t map the arguments to keywords by name. A way to accomplish this in groovy is to accept the keyword arguments as a map:

def foo(Map kwargs, a, b, c='awesome') { [a,b,c,kwargs.d] }
assert foo(1,2,d:'bar') == [1,2,'awesome','bar']

More details on how groovy handles this is here: http://groovy.codehaus.org/Extended+Guide+to+Method+Signatures.