Puppet

Yes, right now the common pattern for this amongst the puppet pro svc folk is referred to as the “underscore-real pattern”, after the workaround they use :

define my::define ($value1 = "string", $value2 = ["dummy array"]) {
    $value2_real_default = [ "Real default1", "Real default2"]

    if $value2[0] != "dummy array" {
        $value2_real = [ $value2_real_default, $value2 ] 
    }
    else {
        $value2_real = [ $value2_real_default ]
    }

    notify { $title:
            message => inline_template('<%= value2_real.join("\n") %>')
    }
}

my::define { 'no_overrides': }
my::define { 'array_override': 
    value2 => [ 'New value1', 'New value2' ]
}

This is… not wonderful. It’d be nice to have some syntax for doing this but I’m not sure what it would look like.

Randall, any thoughts? As I see it, we have a choice: – to control it on the sending side (the array_override resource above would be able to indicate that ‘New value1’ and ‘New value2’ should override whatever my::define provides by default) – control on the receiving side, where my::define gets to decide whether additional parameters to $value2 append to, rather than replacing, what it thinks the defaults should be – refine this code pattern into something polished and worth publishing but don’t make changes into the underlying implementation.