core: add `Sequence::get_or_default` and `get_or_null`

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

diff --git a/lib/core/collection/abstract_collection.nit b/lib/core/collection/abstract_collection.nit
index 309d048..04dabfa 100644 (file)
--- a/lib/core/collection/abstract_collection.nit
+++ b/lib/core/collection/abstract_collection.nit
@@ -859,6 +859,36 @@ interface SequenceRead[E]
                end
        end
 
+       # Try to get an element, return `null` if the `index` is invalid.
+       #
+       # ~~~
+       # var a = [10,20,30]
+       # assert a.get_or_null(1) == 20
+       # assert a.get_or_null(3) == null
+       # assert a.get_or_null(-1) == null
+       # assert a.get_or_null(-10) == null
+       # ~~~
+       fun get_or_null(index: Int): nullable E
+       do
+               if index >= 0 and index < length then return self[index]
+               return null
+       end
+
+       # Try to get an element, return `default` if the `index` is invalid.
+       #
+       # ~~~
+       # var a = [10,20,30]
+       # assert a.get_or_default(1, -1) == 20
+       # assert a.get_or_default(3, -1) == -1
+       # assert a.get_or_default(-1, -1) == -1
+       # assert a.get_or_default(-10, -1) == -1
+       # ~~~
+       fun get_or_default(index: Int, default: E): E
+       do
+               if index >= 0 and index < length then return self[index]
+               return default
+       end
+
        # Get the last item.
        # Is equivalent with `self[length-1]`.
        #