@@ -84,6 +84,21 @@ By definition all objects are +duplicable?+ except +nil+, +false+, +true+, symbo
WARNING. Using +duplicable?+ is discouraged because it depends on a hard-coded list. Classes have means to disallow duplication like removing +dup+ and +clone+ or raising exceptions from them, only +rescue+ can tell.
+The method +returning+ yields its argument to a block and returns it. You tipically use it with a mutable object that gets modified in the block: