We can inspect the number and type of parameters defined for a closure very easily. A closure has the properties maximumNumberOfParameters and parameterTypes for this. So in our code we can ask a closure how many parameters are expected and even which type the parameters are.
// Two simple closure with one and two parameters.
def one = { it.toUpperCase() }
def two = { String s, upper ->
if (upper) {
s.toUpperCase()
} else {
s.toLowerCase()
}
}
def runClosure(cl) {
switch (cl.maximumNumberOfParameters) {
case 1:
assert [java.lang.Object] == cl.parameterTypes
cl.call('Groovy')
break
case 2:
assert [java.lang.String, java.lang.Object] == cl.parameterTypes
cl('Groovy', false)
break
}
}
assert 'GROOVY' == runClosure(one)
assert 'groovy' == runClosure(two)
