Map deepMerge (less readable remix)

test.groovy

def a =  [foo: [foo: true,  bar: true]]
def b =  [foo: [bar: false, baz: true]]

Map.metaClass.deepMerge = { Map other ->
    (delegate.keySet() + other.keySet()).collectEntries { key ->
        def (d, o) = [delegate, other]*.get(key)
        if(d instanceof Map && o instanceof Map) {
            [key, d.deepMerge(o)]
        }
        else {
            [key, o == null ? d : o]
        }
    }
}

a.deepMerge(b)

worse.groovy

Map.metaClass.deepMerge = { Map other ->
    [delegate, other]*.keySet().sum().collectEntries { k ->
        [delegate, other]*.get(k).with { dv, ov ->
            [k, [dv,ov].every { it instanceof Map } ? dv.deepMerge(ov) : (ov == null ? dv : ov)]
        }
    }
}