[Puppet Users] Concatanating result of custom function to a string

Hello,

I'm working on execution of puppet's "puppet cert generate
...--dns_alt_names=name1,name2,name2" using Puppet 2.7.19 and didn't find a
way to figure out the following:

I'd prefer to keep the list of "dns_alt_names" in a puppet array and join()
them when I build the command string.

E.g.
$dns_alt_names = [ 'name1', 'name2', ...]
$command = "puppet cert generate ... --dns_alt_names=" <what goes here?>
join($dns_alt_names, ',').

But I didn't find a way to concatenate the output of the join() call to the
string before it.

A couple of ways I though that might allow this are:

1. Set a temporary variable with the output of join() and interpolate it
into the command with "...${temp_var}"
2. Use inline_template()

Are these the only viable ways to achieve that?

For now I keep the names in a single string, but I think this is less
maintainable than using an array.

Thanks,

--Amos