define if {
  file { "/var/$name": ensure => present }
  $ifarr += $name
}

class foo {
  $ifarr = []
  if {
    "a": ...;
    "b": ...;
  }
  file { "/etc/if": content => inline_template("<% ifarr.each do |val| %> <%= val %>; <% end %>") }
}