infinitered · danielberkompas · May 2, 2016 · May 2, 2016
diff --git a/lib/phoenix_base/maybe.ex b/lib/phoenix_base/maybe.ex
@@ -0,0 +1,82 @@
+defmodule PhoenixBase.Maybe do
+  @moduledoc """
+  Access nested structs, protected from `nil`. See `maybe/1` or `maybe/2` for
+  more details.
+
+  ## Example
+
+      import PhoenixBase.Maybe
+
+      map = %{city: %{name: "Portland"}}
+      maybe(map, [:city, :name]) # => "Portland"
+      maybe(map.city.name) # => "Portland"
+      maybe(map.city.location) # => nil
+
+  """
+
+  @doc """
+  Get a value out of a nested map or struct, or return nil. Compiles down to
+  `maybe/2`. In other words, this:
+
+      maybe(map.city.name)
+
+  Is compiled down to a simple function call to `maybe/2`:
+
+      maybe(map, [:city, :name])
+
+  ## Examples
+
+      iex> map = %{city: %{name: "Portland"}}
+      ...> maybe(map.city.name)
+      "Portland"
+
+      iex> map = %{city: nil}
+      ...> maybe(map.city.name)
+      nil
+  """
+  defmacro maybe(ast) do
+    [variable|keys] = extract_keys(ast)
+
+    quote do
+      maybe(var!(unquote(variable)), unquote(keys))
+    end
+  end
+
+  @doc """
+  Get a value out of a nested map or struct, or return nil. For prettier syntax,
+  see the `maybe/1` macro.
+
+  ## Examples
+
+      iex> map = %{city: %{name: "Portland"}}
+      ...> maybe(map, [:city, :name])
+      "Portland"
+
+      iex> maybe(%{}, [:city, :name])
+      nil
+  """
+  @spec maybe(map, [atom]) :: any | nil
+  def maybe(nil, _keys), do: nil
+  def maybe(val, []), do: val
+  def maybe(map, [h|t]) do
+    maybe(Map.get(map, h), t)
+  end
+
+  defp extract_keys(ast, keys \\ [])
+  defp extract_keys([], keys), do: keys
+  defp extract_keys({{:., _, args}, _, _}, keys) do
+    extract_keys(args, keys)
+  end
+  defp extract_keys([{{:., _, args}, _, _}|t], keys) do
+    keys = keys ++ extract_keys(args)
+    extract_keys(t, keys)
+  end
+  defp extract_keys([{:., _, args}|t], keys) do
+    keys = keys ++ extract_keys(args)
+    extract_keys(t, keys)
+  end
+  defp extract_keys([key|t], keys) do
+    keys = keys ++ [key]
+    extract_keys(t, keys)
+  end
+end
diff --git a/test/phoenix_base/maybe_test.exs b/test/phoenix_base/maybe_test.exs
@@ -0,0 +1,7 @@
+defmodule PhoenixBase.MaybeTest do
+  use ExUnit.Case
+
+  import PhoenixBase.Maybe
+
+  doctest PhoenixBase.Maybe
+end
diff --git a/web/web.ex b/web/web.ex
@@ -54,6 +54,9 @@ defmodule PhoenixBase.Web do
       import PhoenixBase.Router.Helpers
       import PhoenixBase.ErrorHelpers
       import PhoenixBase.Gettext
+
+      # Import Maybe, as it's common to want nil protection in views
+      import PhoenixBase.Maybe
     end
   end