Hello everyone,

I wrote a small library today called MapDiff. It returns a map listing the (smallest amount of) changes to get from map_a to map_b:

iex> foo = %{a: 1, b: 2, c: %{d: 3, e: 4, f: 5}}
iex> bar = %{a: 1, b: 42, c: %{d: %{something_else: "entirely"}, f: 10}}
iex> MapDiff.diff(foo, bar)
%{changed: :map_change,
  value: %{a: %{changed: :equal, value: 1},
    b: %{added: 42, changed: :primitive_change, removed: 2},
    c: %{changed: :map_change,
      value: %{d: %{added: %{something_else: "entirely"},
      changed: :primitive_change, removed: 3},
    e: %{changed: :removed, value: 4},
    f: %{added: 10, changed: :primitive_change, removed: 5}}}}}

This is mainly useful if you have two maps describing the state of something, where replacing all of the old state and then filling in the new is too slow, which means that only replacing the things that actually are changed is better.