Pattern match function against empty map

Question

I\'m playing around with pattern match and I found out, that it\'s not quite easy to pattern match parameters of a method against an empty map. I thought it would go somethi

Answer 1

In addition to @PatrickOscity's answer (which I would use for an empty map), you can use a map_size/1 guard to match against maps with a number of keys:

defmodule PatternMatch do
  def modify(map) when map_size(map) == 0 do
    %{}
  end

  def modify(map) when map_size(map) == 1 do
    #something else
  end

  def modify(map) do
    # expensive operation
    %{ modified: "map" }
  end
end

Here is an output from iex using Kernel.match?/2 to show map_size/1 in action:

iex(6)> Kernel.match?(map when map_size(map) == 1, %{})
false
iex(7)> Kernel.match?(map when map_size(map) == 1, %{foo: "bar"})
true