lua: simple tag cache enabling factoring way_function into smaller functions

profiles/lib/tag_cache.lua

@@ -0,0 +1,35 @@
+TagCache = {}
+
+function TagCache.get(data, key)
+  local v = data.cache[key]
+  if v then
+    if v == '' then
+      return nil
+    else
+      return v
+    end
+  else
+    v = data.way:get_value_by_key(key)
+    if v == nil then
+      data.cache[key] = ''
+      return nil
+    else
+      data.cache[key] = v
+      if v == '' then
+        return nil
+      else
+        return v
+      end
+    end
+  end
+end
+
+function TagCache.set(data,key,value)
+  if value then
+    data.cache[key] = value
+  else
+    data.cache[key] = ''
+  end    
+end
+
+return TagCache