Groovyから簡潔にOptionalを操作する例(an example of handling optional from groovy)

Java8Groovy.groovy

import java.util.Optional

class Java8Groovy {

    void test() {
        Optional<Integer> firstName = Optional.of("FirstName")
        Optional<Integer> lastName = Optional.of("LastName")
        Optional NULL = Optional.empty()
        assert (lastName + " " + firstName).get() == "LastName FirstName"
        assert (NULL     + " " + firstName) == NULL
        assert (lastName + " " + NULL) == NULL
        assert (NULL     + " " + NULL) == NULL
    }

    public static void main(String[] a) {
        Optional.metaClass.methodMissing = { String name, Object args ->
            assert args instanceof Object[]
            for (int i=0; i<args.size(); i++) {
                if (args[i] instanceof Optional) {
                    if (args[i].isPresent()) {
                        args[i] = args[i].get()
                    }
                    else {
                        return Optional.empty()
                    }
                }
            }
            if (delegate.isPresent()) {
                return Optional.ofNullable(delegate.get().invokeMethod(name, args))
            }
            else {
                return Optional.empty()
            }
        }
        new Java8Groovy().test();
    }
}