--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/stdlib/lib/puppet/functions/merge.rb	Sun Jan 26 11:36:07 2020 +0000
@@ -0,0 +1,110 @@
+# @summary
+#   Merges two or more hashes together or hashes resulting from iteration, and returns
+#   the resulting hash.
+#
+# @example Using merge()
+#   $hash1 = {'one' => 1, 'two', => 2}
+#   $hash2 = {'two' => 'dos', 'three', => 'tres'}
+#   $merged_hash = merge($hash1, $hash2) # $merged_hash =  {'one' => 1, 'two' => 'dos', 'three' => 'tres'}
+#
+# When there is a duplicate key, the key in the rightmost hash will "win."
+#
+# Note that since Puppet 4.0.0 the same merge can be achieved with the + operator.
+#  `$merged_hash = $hash1 + $hash2`
+#
+# If merge is given a single Iterable (Array, Hash, etc.) it will call a given block with
+# up to three parameters, and merge each resulting Hash into the accumulated result. All other types
+# of values returned from the block (typically undef) are skipped (not merged).
+#
+# The codeblock can take 2 or three parameters:
+# * with two, it gets the current hash (as built to this point), and each value (for hash the value is a [key, value] tuple)
+# * with three, it gets the current hash (as built to this point), the key/index of each value, and then the value
+#
+# If the iterable is empty, or no hash was returned from the given block, an empty hash is returned. In the given block, a call to `next()`
+# will skip that entry, and a call to `break()` will end the iteration.
+#
+# @example counting occurrences of strings in an array
+#   ['a', 'b', 'c', 'c', 'd', 'b'].merge | $hsh, $v | { { $v => $hsh[$v].lest || { 0 } + 1 } } # results in { a => 1, b => 2, c => 2, d => 1 }
+#
+# @example skipping values for entries that are longer than 1 char
+#   ['a', 'b', 'c', 'c', 'd', 'b', 'blah', 'blah'].merge | $hsh, $v | { if $v =~ String[1,1] { { $v => $hsh[$v].lest || { 0 } + 1 } } } # results in { a => 1, b => 2, c => 2, d => 1 }
+#
+# The iterative `merge()` has an advantage over doing the same with a general `reduce()` in that the constructed hash
+# does not have to be copied in each iteration and thus will perform much better with large inputs.
+Puppet::Functions.create_function(:merge) do
+  # @param args
+  #   Repeated Param - The hashes that are to be merged
+  #
+  # @return
+  #   The merged hash
+  dispatch :merge2hashes do
+    repeated_param 'Variant[Hash, Undef, String[0,0]]', :args # this strange type is backwards compatible
+    return_type 'Hash'
+  end
+
+  # @param args
+  #   Repeated Param - The hashes that are to be merged
+  #
+  # @param block
+  #   A block placed on the repeatable param `args`
+  #
+  # @return
+  #   The merged hash
+  dispatch :merge_iterable3 do
+    repeated_param 'Iterable', :args
+    block_param 'Callable[3,3]', :block
+    return_type 'Hash'
+  end
+
+  # @param args
+  #   Repeated Param - The hashes that are to be merged
+  #
+  # @param block
+  #   A block placed on the repeatable param `args`
+  #
+  # @return
+  #   The merged hash
+  dispatch :merge_iterable2 do
+    repeated_param 'Iterable', :args
+    block_param 'Callable[2,2]', :block
+    return_type 'Hash'
+  end
+
+  def merge2hashes(*hashes)
+    accumulator = {}
+    hashes.each { |h| accumulator.merge!(h) if h.is_a?(Hash) }
+    accumulator
+  end
+
+  def merge_iterable2(iterable)
+    accumulator = {}
+    enum = Puppet::Pops::Types::Iterable.asserted_iterable(self, iterable)
+    enum.each do |v|
+      r = yield(accumulator, v)
+      accumulator.merge!(r) if r.is_a?(Hash)
+    end
+    accumulator
+  end
+
+  def merge_iterable3(iterable)
+    accumulator = {}
+    enum = Puppet::Pops::Types::Iterable.asserted_iterable(self, iterable)
+    if enum.hash_style?
+      enum.each do |entry|
+        r = yield(accumulator, *entry)
+        accumulator.merge!(r) if r.is_a?(Hash)
+      end
+    else
+      begin
+        index = 0
+        loop do
+          r = yield(accumulator, index, enum.next)
+          accumulator.merge!(r) if r.is_a?(Hash)
+          index += 1
+        end
+      rescue StopIteration # rubocop:disable Lint/HandleExceptions
+      end
+    end
+    accumulator
+  end
+end