[util] Add a decorators utility module.

compiler_gym/util/BUILD

@@ -11,6 +11,7 @@ py_library(
         "__init__.py",
         "capture_output.py",
         "debug_util.py",
+        "decorators.py",
         "download.py",
         "logs.py",
         "minimize_trajectory.py",

compiler_gym/util/decorators.py

@@ -0,0 +1,29 @@
+# Copyright (c) Facebook, Inc. and its affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+import functools
+from typing import Any, Callable
+
+
+def memoized_property(func: Callable[..., Any]) -> Callable[..., Any]:
+    """A property decorator that memoizes the result.
+
+    This is used to memoize the results of class properties, to be used when
+    computing the property value is expensive.
+
+    :param func: The function which should be made to a property.
+
+    :returns: The decorated property function.
+    """
+    attribute_name = "_memoized_property_" + func.__name__
+
+    @property
+    @functools.wraps(func)
+    def decorator(self):
+        if not hasattr(self, attribute_name):
+            setattr(self, attribute_name, func(self))
+
+        return getattr(self, attribute_name)
+
+    return decorator