1 files changed, 61 insertions, 0 deletions
diff --git a/django/utils/functional.py b/django/utils/functional.py
index f3b0598763..2b3ca8293e 100644
--- a/django/utils/functional.py
+++ b/django/utils/functional.py
@@ -2,3 +2,64 @@ def curry(*args, **kwargs):
     def _curried(*moreargs, **morekwargs):
         return args[0](*(args[1:]+moreargs), **dict(kwargs.items() + morekwargs.items()))
     return _curried
+
+def lazy(func, *resultclasses):
+
+    """
+    lazy turns any callable passed in into a lazy evaluated callable.
+    you need to give result classes or types - at least one is needed
+    so that the automatic forcing of the lazy evaluation code is
+    triggered. Results are not memoized - the function is evaluated
+    on every access.
+    """
+
+    class __proxy__:
+    
+        """
+        This inner class encapsulates the code that should be evaluated
+        lazyly. On calling of one of the magic methods it will force
+        the evaluation and store the result - afterwards the result
+        is delivered directly. So the result is memoized.
+        """
+
+        def __init__(self, args, kw):
+           self.__func = func
+           self.__args = args
+           self.__kw = kw
+           self.__dispatch = {}
+           for resultclass in resultclasses:
+               self.__dispatch[resultclass] = {}
+               for (k, v) in resultclass.__dict__.items():
+                   setattr(self, k, self.__promise__(resultclass, k, v))
+	
+        def __promise__(self, klass, funcname, func):
+        
+            """
+            This function builds a wrapper around some magic method and
+            registers that magic method for the given type and methodname.
+            """
+    
+            def __wrapper__(*args, **kw):
+                """
+                This wrapper function automatically triggers the evaluation of
+                a lazy value. It then applies the given magic method of the
+                result type.
+                """
+                res = self.__func(*self.__args, **self.__kw)
+                return self.__dispatch[type(res)][funcname](res, *args, **kw)
+  
+            if not self.__dispatch.has_key(klass):
+                self.__dispatch[klass] = {}
+            self.__dispatch[klass][funcname] = func
+            return __wrapper__
+  
+    def __wrapper__(*args, **kw):
+        """
+        This wrapper function just creates the proxy object that is returned
+        instead of the actual value.
+        """
+        return __proxy__(args, kw)
+
+    return __wrapper__
+
+