lib/core: add Sequence::modulo to access with a Python-wrap semantic

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 f77d8f4..5f9af05 100644 (file)
--- a/lib/core/collection/abstract_collection.nit
+++ b/lib/core/collection/abstract_collection.nit
@@ -812,6 +812,44 @@ interface SequenceRead[E]
        # REQUIRE `index >= 0 and index < length`
        fun [](index: Int): E is abstract
 
+       # Return the index-th element but wrap
+       #
+       # Whereas `self[]` requires the index to exists, the `modulo` accessor automatically
+       # wraps overbound and underbouds indexes.
+       #
+       # ~~~
+       # var a = [10,20,30]
+       # assert a.modulo(1) == 20
+       # assert a.modulo(3) == 10
+       # assert a.modulo(-1) == 30
+       # assert a.modulo(-10) == 30
+       # ~~~
+       #
+       # REQUIRE `not_empty`
+       # ENSURE `result == self[modulo_index(index)]`
+       fun modulo(index: Int): E do return self[modulo_index(index)]
+
+       # Returns the real index for a modulo index.
+       #
+       # ~~~
+       # var a = [10,20,30]
+       # assert a.modulo_index(1) == 1
+       # assert a.modulo_index(3) == 0
+       # assert a.modulo_index(-1) == 2
+       # assert a.modulo_index(-10) == 2
+       # ~~~
+       #
+       # REQUIRE `not_empty`
+       fun modulo_index(index: Int): Int
+       do
+               var length = self.length
+               if index >= 0 then
+                       return index % length
+               else
+                       return length - (-1 - index) % length - 1
+               end
+       end
+
        # Get the last item.
        # Is equivalent with `self[length-1]`.
        #
@@ -1062,6 +1100,24 @@ interface Sequence[E]
        # REQUIRE `index >= 0 and index <= length`
        fun []=(index: Int, item: E) is abstract
 
+       # Set the index-th element but wrap
+       #
+       # Whereas `self[]=` requires the index to exists, the `modulo` accessor automatically
+       # wraps overbound and underbouds indexes.
+       #
+       # ~~~
+       # var a = [10,20,30]
+       # a.modulo(1) = 200
+       # a.modulo(3) = 100
+       # a.modulo(-1) = 300
+       # a.modulo(-10) = 301
+       # assert a == [100, 200, 301]
+       # ~~~
+       #
+       # REQUIRE `not_empty`
+       # ENSURE `self[modulo_index(index)] == value`
+       fun modulo=(index: Int, value: E) do self[modulo_index(index)] = value
+
        # Insert an element at a given position, following elements are shifted.
        #
        #     var a = [10, 20, 30, 40]