1 files changed, 51 insertions, 0 deletions
diff --git a/lib/gears/cache.lua b/lib/gears/cache.lua
new file mode 100644
index 0000000..dc5add5
--- /dev/null
+++ b/lib/gears/cache.lua
@@ -0,0 +1,51 @@
+---------------------------------------------------------------------------
+-- @author Uli Schlachter
+-- @copyright 2015 Uli Schlachter
+-- @classmod gears.cache
+---------------------------------------------------------------------------
+
+local select = select
+local setmetatable = setmetatable
+local unpack = unpack or table.unpack -- luacheck: globals unpack (compatibility with Lua 5.1)
+
+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