How do you concatenate strings in a Puppet .pp file?

Here is my naive approach:

# puppet/init.pp
$x = 'hello ' + 
     'goodbye'

This does not work. How does one concatenate strings in Puppet?

Keyword variable interpolation:

$value = "${one}${two}"

Source: http://docs.puppetlabs.com/puppet/4.3/reference/lang_variables.html#interpolation

Note that although it might work without the curly braces, you should always use them.

I use the construct where I put the values into an array an then 'join' them. In this example my input is an array and after those have been joined with the ':2181,' the resulting value is again put into an array that is joined with an empty string as separator.

$zookeeperservers = [ 'node1.example.com', 'node2.example.com', 'node3.example.com' ]
$mesosZK = join([ "zk://" , join($zookeeperservers,':2181,') ,":2181/mesos" ],'')

resulting value of $mesosZK

zk://node1.example.com:2181,node2.example.com:2181,node3.example.com:2181/mesos