Merge pull request #3 from vesta-merkur/pinned_vars

Allow for pinned variables in pattern

README.md

@@ -94,6 +94,24 @@ def handle_info({:hello, name}, state) do
 end
 ```
 
+### Using local variables
+
+Sometimes one wish to subscribe using a pattern involving local variables.
+The `subscribe` macro accepts a `bind_quoted` argument, that will replace pinned variables with the given values.
+
+E.g.
+
+```elixir
+size = 42
+Hub.subscribe("my channel", %{size: ^size}, bind_quoted: [size: size])
+```
+
+is equivalent to
+
+```elixir
+Hub.subscribe("my channel", %{size: 42})
+```
+
 ## Examples
 
 Subscribe only once to a message:

lib/hub.ex

@@ -48,7 +48,10 @@ defmodule Hub do
   """
   defmacro subscribe(channel, pattern, options \\ []) do
     quote do
-      Hub.subscribe_quoted(unquote(channel), unquote(Macro.escape(pattern)), unquote(options))
+      {bind_quoted, options} = unquote(options) |> Keyword.pop(:bind_quoted, [])
+      quoted_pattern = unquote(Macro.escape(pattern)) |> Hub.replace_pins(bind_quoted)
+
+      Hub.subscribe_quoted(unquote(channel), quoted_pattern, options)
     end
   end
 
@@ -145,4 +148,27 @@ defmodule Hub do
   defp tracker_topic(channel) when is_binary(channel) do
     @tracker_topic_prefix <> channel
   end
+
+  @doc false
+  def replace_pins({:^, _, [{name, _, _}]} = term, bindings) do
+    case Keyword.fetch(bindings, name) do
+      {:ok, value} -> value
+      :error -> term
+    end
+  end
+  def replace_pins({fun, con, args}, bindings) do
+    {fun, con, replace_pins(args, bindings)}
+  end
+  def replace_pins({term_1, term_2}, bindings) do
+    {
+      replace_pins(term_1, bindings),
+      replace_pins(term_2, bindings)
+    }
+  end
+  def replace_pins(list, bindings) when is_list(list) do
+    list |> Enum.map(&replace_pins(&1, bindings))
+  end
+  def replace_pins(term, _bindings) do
+    term
+  end
 end

test/hub_test.exs

@@ -124,4 +124,12 @@ defmodule HubTest do
     result = Task.await(task)
     assert result == ~w(Me You)
   end
+
+  test "local variables parts of pattern" do
+    name = "World"
+    Hub.subscribe("global", {:hello, ^name}, bind_quoted: [name: name])
+    Hub.publish("global", {:hello, "World"})
+
+    assert_received({:hello, "World"})
+  end
 end