kernel: new interface `Cloneable` to provide a `clone` method

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/lib/standard/kernel.nit b/lib/standard/kernel.nit
index 5cc0547..21b0fc1 100644 (file)
--- a/lib/standard/kernel.nit
+++ b/lib/standard/kernel.nit
@@ -226,6 +226,25 @@ interface Discrete
        end
 end
 
+# Something that can be cloned
+#
+# This interface introduces the `clone` method used to duplicate an instance
+# Its specific semantic is let to the subclasses.
+interface Cloneable
+       # Duplicate `self`
+       #
+       # The specific semantic of this method is let to the subclasses;
+       # Especially, if (and how) attributes are cloned (depth vs. shallow).
+       #
+       # As a rule of thumb, the principle of least astonishment should
+       # be used to guide the semantic.
+       #
+       # Note that as the returned clone depends on the semantic,
+       # the `==` method, if redefined, should ensure the equality
+       # between an object and its clone.
+       fun clone: SELF is abstract
+end
+
 # A numeric value supporting mathematical operations
 interface Numeric
        super Comparable