lec03 generic servers

lectures/03/rcounter/lib/counter/worker.ex

@@ -0,0 +1,43 @@
+defmodule Counter.Worker do
+    use GenServer # use builtint Elixir Generic Server
+
+    ### Client API ###
+    def inc(amt \\ 1) do
+      GenServer.cast(__MODULE__, {:inc, amt})
+    end
+
+    def dec(amt \\ 1) do
+        GenServer.cast(__MODULE__, {:dec, amt})
+    end
+
+    def value() do
+      GenServer.call(__MODULE__, :value)
+    end
+
+    ### Server Impl ###
+    def start(n \\ 0) do
+        # use module name as name for registered server
+        # now inc, dec, and value dont need pid, and can use __MODULE__
+        GenServer.start(__MODULE__, n, name: __MODULE__)
+    end
+
+    @impl true       # annotation that signature agrees with callback
+    def init(arg) do # arg comes from 2nd arg of GenServer.start
+        {:ok, arg}
+    end
+
+    @impl true
+    def handle_call(:value, _from, state) do
+      {:reply, state, state} # {:reply, actual_reply, new_state}
+    end
+
+    @impl true
+    def handle_cast({:inc, amt}, state) do
+        {:noreply, state + amt} # {:noreply, new_state}
+    end
+
+    @impl true
+    def handle_cast({:dec, amt}, state) do
+        {:noreply, state - amt} # {:noreply, new_state}
+    end
+end