Add a generic cache system as gears.cache

Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/gears/cache.lua

@@ -0,0 +1,52 @@
+---------------------------------------------------------------------------
+-- @author Uli Schlachter
+-- @copyright 2015 Uli Schlachter
+-- @release @AWESOME_VERSION@
+-- @classmod gears.cache
+---------------------------------------------------------------------------
+
+local select = select
+local setmetatable = setmetatable
+local unpack = unpack or table.unpack
+
+local cache = {}
+
+--- Get an entry from the cache, creating it if it's missing.
+-- @param ... Arguments for the creation callback. These are checked against the
+--            cache contents for equality.
+-- @return The entry from the cache
+function cache:get(...)
+    local result = self._cache
+    for i = 1, select("#", ...) do
+        local arg = select(i, ...)
+        local next = result[arg]
+        if not next then
+            next = {}
+            result[arg] = next
+        end
+        result = next
+    end
+    local ret = result._entry
+    if not ret then
+        ret = { self._creation_cb(...) }
+        result._entry = ret
+    end
+    return unpack(ret)
+end
+
+--- Create a new cache object. A cache keeps some data that can be
+-- garbage-collected at any time, but might be useful to keep.
+-- @param creation_cb Callback that is used for creating missing cache entries.
+-- @return A new cache object.
+function cache.new(creation_cb)
+    return setmetatable({
+        _cache = setmetatable({}, { __mode = "v" }),
+        _creation_cb = creation_cb
+    }, {
+        __index = cache
+    })
+end
+
+return setmetatable(cache, { __call = function(_, ...) return cache.new(...) end })
+
+-- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80

lib/gears/init.lua

@@ -15,6 +15,7 @@ return
     surface = require("gears.surface");
     wallpaper = require("gears.wallpaper");
     timer = require("gears.timer");
+    cache = require("gears.cache");
 }
 
 -- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80

spec/gears/cache_spec.lua

@@ -0,0 +1,61 @@
+---------------------------------------------------------------------------
+-- @author Uli Schlachter
+-- @copyright 2015 Uli Schlachter
+---------------------------------------------------------------------------
+
+local cache = require("gears.cache")
+
+describe("gears.cache", function()
+    -- Make sure no cache is cleared during the tests
+    before_each(function()
+        collectgarbage("stop")
+    end)
+    after_each(function()
+        collectgarbage("restart")
+    end)
+
+    describe("Zero arguments", function()
+        it("Creation cb is called", function()
+            local called = false
+            local c = cache(function()
+                called = true
+            end)
+            local res = c:get()
+            assert.is_nil(res)
+            assert.is_true(called)
+        end)
+    end)
+
+    describe("Two arguments", function()
+        it("Cache works", function()
+            local num_calls = 0
+            local c = cache(function(a, b)
+                num_calls = num_calls + 1
+                return a + b
+            end)
+            local res1 = c:get(1, 2)
+            local res2 = c:get(1, 3)
+            local res3 = c:get(1, 2)
+            assert.is.equal(res1, 3)
+            assert.is.equal(res2, 4)
+            assert.is.equal(res3, 3)
+            assert.is.equal(num_calls, 2)
+        end)
+
+        it("Cache invalidation works", function()
+            local num_calls = 0
+            local c = cache(function(a, b)
+                num_calls = num_calls + 1
+                return a + b
+            end)
+            local res1 = c:get(1, 2)
+            collectgarbage("collect")
+            local res2 = c:get(1, 2)
+            assert.is.equal(res1, 3)
+            assert.is.equal(res2, 3)
+            assert.is.equal(num_calls, 2)
+        end)
+    end)
+end)
+
+-- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80