Groovy convert from List to var args for method call

Question

I am using a plugin that provides email functionality as follows:

class SendSesMail {

    //to
    void to(String ... _to) { 
        this.to?.addAll(_to)
        log.debug "Setting 'to' addresses to ${this.to}"
    }

}

The documentation states the class is called as follows:

sesMail {
    from "[email protected]"
    replyTo "[email protected]"
    to "[email protected]", "[email protected]", "[email protected]"
    subject "Subject"
    html "Body HTML"
}

In the code a List of addresses is built up and I'm trying to figure out how to convert this list to the var args expected by the method.

Converting to a String concatenated with "," doesn't work as this is an invalid email address. I need to be able to separate each List item into a separate parameter to avoid having to iterate over the List and send each email individually.

Solution

Probably the spread operator, *, is what you're looking for:

def to(String... emails) {
    emails.each { println "Sending email to: $it"}
}

def emails = ["[email protected]", "[email protected]", "[email protected]"]
to(*emails)
// Output: 
// Sending email to: [email protected]
// Sending email to: [email protected]
// Sending email to: [email protected]

Notice that the parentheses on the method call to to are mandatory, as otherwise to *emails would be parsed as a multiplication. Bad choice of overloaded grammar symbols IMO =P