[#92] Add :default option to incr/3

lib/nebulex/adapters/local.ex

@@ -274,6 +274,7 @@ defmodule Nebulex.Adapters.Local do
   # Inherit default persistence implementation
   use Nebulex.Adapter.Persistence
 
+  import Nebulex.Helpers
   import Record
 
   alias Nebulex.Adapters.Local.{Backend, Generation, Metadata}
@@ -485,13 +486,15 @@ defmodule Nebulex.Adapters.Local do
   end
 
   @impl true
-  def incr(%{meta_tab: meta_tab, backend: backend, stat_counter: ref}, key, incr, ttl, _opts) do
+  def incr(%{meta_tab: meta_tab, backend: backend, stat_counter: ref}, key, incr, ttl, opts) do
+    default = get_option(opts, :default, &is_integer/1, 0)
+
     meta_tab
     |> newer_gen()
     |> backend.update_counter(
       key,
       {3, incr},
-      entry(key: key, value: 0, touched: Time.now(), ttl: ttl)
+      entry(key: key, value: default, touched: Time.now(), ttl: ttl)
     )
     |> update_stats(:write, ref)
   end

lib/nebulex/cache.ex

@@ -823,6 +823,10 @@ defmodule Nebulex.Cache do
       (or expiry time) for the given key  in **milliseconds**. Defaults
       to `:infinity`.
 
+    * `:default` - If `key` is not present in Cache, the default value is
+      inserted as initial value of key before the it is incremented.
+      Defaults to `0`.
+
   See the "Shared options" section at the module documentation for more options.
 
   ## Examples
@@ -835,6 +839,9 @@ defmodule Nebulex.Cache do
 
       iex> MyCache.incr(:a, -1)
       2
+
+      iex> MyCache.incr(:missing_key, 2, default: 10)
+      12
   """
   @callback incr(key, incr :: integer, opts) :: integer
 

test/shared/cache/entry_test.exs

@@ -252,6 +252,12 @@ defmodule Nebulex.Cache.EntryTest do
       end
     end
 
+    test "incr with default", %{cache: cache} do
+      assert cache.incr(:counter1, 1, default: 10) == 11
+      assert cache.incr(:counter2, 2, default: 10) == 12
+      assert cache.incr(:counter3, -2, default: 10) == 8
+    end
+
     ## Helpers
 
     defp to_int(data) when is_integer(data), do: data