Closures

When a function is not expected to be used more than once and is simple enough to fit in one statement, you can define such a validator or a converter as a closure, for example:

guestsNum toInt >> {it > 1}

The it variable inside the closure refers to a value passed from a previous subrule (here toInt). Also, since closures are part of the rules you have an access to all input parameters, e.g.:

adminsNum toInt
guestsNum toInt >> {guestsNum + adminsNum < maxUsersNum}

You can also use a closure validator or converter to explicitly define all function parameters, for example, to run a function against a parameter that is not the default for a current rule.

Validator and converter calls that occur in a closure body are handled as general Groovy method calls and thus all function arguments must be specified. For example:

// expectedChildrenNum is a method that takes one argument
expectedGuestsNum toInt >> {it + expectedChildrenNum(it)} 

Using a closure you can easily assign a constant value to a parameter, for example:

tempParameter {7}