first commit

lib/knife/memoize.lua

@@ -0,0 +1,77 @@
+local loadstring = _G.loadstring or _G.load
+local weakKeys = { __mode = 'k' }
+local cache = setmetatable({}, weakKeys)
+local resultsKey = {}
+local nilKey = {}
+
+local function getMetaCall (callable)
+    local meta = getmetatable(callable)
+    return meta and meta.__call
+end
+
+local tupleConstructorCache = {}
+
+local function buildTupleConstructor (n)
+    if tupleConstructorCache[n] then
+        return tupleConstructorCache[n]
+    end
+    local t = {}
+    for i = 1, n do
+        t[i] = "a" .. i
+    end
+    local args = table.concat(t, ',')
+    local ctor = loadstring('return function(' .. args ..
+        ') return function() return ' .. args .. ' end end')()
+    tupleConstructorCache[n] = ctor
+    return ctor
+end
+
+local function tuple (...)
+    return buildTupleConstructor(select('#', ...))(...)
+end
+
+return function (callable)
+    local metaCall = getMetaCall(callable)
+
+    if type(callable) ~= 'function' and not metaCall then
+        error 'Attempted to memoize a non-callable value.'
+    end
+
+    cache[callable] = setmetatable({}, weakKeys)
+
+    local function run (...)
+        local node = cache[callable]
+        local argc = select('#', ...)
+        for i = 1, argc do
+            local key = select(i, ...)
+            if key == nil then
+                key = nilKey
+            end
+            if not node[key] then
+                node[key] = setmetatable({}, weakKeys)
+            end
+            node = node[key]
+        end
+
+        if not node[resultsKey] then
+            node[resultsKey] = tuple(callable(...))
+        end
+
+        return node[resultsKey]()
+    end
+
+    if metaCall then
+        return function (...)
+            local call = getMetaCall(callable)
+
+            if call ~= metaCall then
+                cache[callable] = setmetatable({}, weakKeys)
+                metaCall = call
+            end
+
+            return run(...)
+        end, cache, resultsKey, nilKey
+    end
+
+    return run, cache, resultsKey, nilKey
+end