58. Named Arguments

You can use named arguments by having the first parameter be a Map. Consider the method below:

def displayMessage (options, message) {

    def borderText = ''
    if (! options.containsKey('border') || options.border) {
        borderText = '--------------------------'
    }

    def title = 'Important message:'
    if (options.title) {
        title = options.title
    }

    println """\
	    $borderText
	    $title
	    \t $message
	    $borderText
	    """
}

displayMessage(title: 'Canberra', border: true, 'The capital of Australia')

The options parameter is actually a Map and this lets the caller use an interesting Groovy syntax when calling the method. Instead of passing a Map ([:]) to the options parameter, the caller can use the key: value format in their method call. This lets us call displayMessage in many ways, including:

• displayMessage(title: 'Canberra', border: true, 'The capital of Australia')
• displayMessage title: 'Time', "It is now ${new Date()}"
• displayMessage border: false, 'Hang in there little buddy!'

My recommendation is to use named parameters for non-essential parameters and to make sure that your method can operate correctly if a named parameter is not provided.

If others are to be using your method or you need to remember which named parameters are available, then you’ll make sure that you add some useful documentation to the method.