lib/gc: intro `FinalizableOnce`

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --git a/lib/standard/gc.nit b/lib/standard/gc.nit
index acee1f6..23fa47f 100644 (file)
--- a/lib/standard/gc.nit
+++ b/lib/standard/gc.nit
@@ -36,3 +36,29 @@ class Finalizable
        # to use attributes of this instances.
        fun finalize do end
 end
+
+# An object to be finalized only once
+#
+# This is an utility sub-class to `Finalizable` which ensures that `finalized_once`
+# is called only once per instance. User classes implementing `FinalizableOnce`
+# shoud specialize `finalize_once` and _not_ `finalize`. When manipulating the user
+# class, only `finalize` should be called as it protects `finalize_once`.
+class FinalizableOnce
+       super Finalizable
+
+       # Has `self` been finalized? (either by the GC or an explicit call to `finalize`)
+       var finalized = false
+
+       redef fun finalize
+       do
+               if finalized then return
+
+               finalize_once
+               finalized = true
+       end
+
+       # Real finalization method of `FinalizableOnce`, will be called only once
+       #
+       # See: `Finalizable::finalize` for restrictions on finalizer methods.
+       protected fun finalize_once do end
+end