Generic Slices (#544)

* Changed slice fields to generics, added check to adjust_indices

* fix typecheck

* Refactored Slice class, fixed test

* fix test

* made slice fields optional, updated tests

* Fix list optimization for new slices; update tests

---------

Co-authored-by: A. R. Shajii <ars@ars.me>

codon/cir/transform/pythonic/list.cpp

@@ -14,7 +14,7 @@ namespace pythonic {
 namespace {
 
 static const std::string LIST = "std.internal.types.ptr.List";
-static const std::string SLICE = "std.internal.types.slice.Slice";
+static const std::string SLICE = "std.internal.types.slice.Slice[int,int,int]";
 
 bool isList(Value *v) { return v->getType()->getName().rfind(LIST + "[", 0) == 0; }
 bool isSlice(Value *v) { return v->getType()->getName() == SLICE; }

stdlib/internal/types/slice.codon

@@ -2,14 +2,36 @@
 
 @tuple
 class Slice:
-    start: Optional[int]
+    start: Optional[T]
-    stop: Optional[int]
+    stop: Optional[U]
-    step: Optional[int]
+    step: Optional[V]
+    T: type
+    U: type
+    V: type
 
-    def __new__(stop: Optional[int]):
+    def __new__(stop: Optional[U], U: type = int):
         return Slice(None, stop, None)
 
+    def __new__(
+            start: Optional[T],
+            stop: Optional[U],
+            T: type = int,
+            U: type = int):
+        return Slice(start, stop, None)
+
+    def __new__(
+            start: Optional[T],
+            stop: Optional[U],
+            step: Optional[V],
+            T: type = int,
+            U: type = int,
+            V: type = int) -> Slice[T, U, V]:
+        return (start, stop, step)
+
     def adjust_indices(self, length: int) -> Tuple[int, int, int, int]:
+        if not (T is int and U is int and V is int):
+            compile_error("slice indices must be integers or None")
+
         step: int = self.step if self.step is not None else 1
         start: int = 0
         stop: int = 0
@@ -58,4 +80,10 @@ class Slice:
     def __repr__(self):
         return f"slice({self.start}, {self.stop}, {self.step})"
 
+    def __eq__(self, other: Slice):
+        return self.start == other.start and self.step == other.step and self.stop == other.stop
+
+    def __ne__(self, other: Slice):
+        return not self.__eq__(other)
+
 slice = Slice

test/core/containers.codon

@@ -764,6 +764,40 @@ def test_slice():
     x = X(tmp)
     x[1:2] = 42
     assert tmp == [(slice(1, 2), 42)]
+
+    # Non-int elements
+    def check_types(s, T: type, U: type, V: type):
+        return (type(s.start) is Optional[T] and
+                type(s.stop) is Optional[U] and
+                type(s.step) is Optional[V])
+    assert check_types(slice(1j, 'x', 3.14), complex, str, float)
+    assert check_types(slice(None, 'x', 3.14), int, str, float)
+    assert check_types(slice(1j, None, 3.14), complex, int, float)
+    assert check_types(slice(1j, 'x', None), complex, str, int)
+    assert check_types(slice(1j, None, None), complex, int, int)
+    assert check_types(slice(None, 'x', None), int, str, int)
+    assert check_types(slice(None, None, 3.14), int, int, float)
+    assert check_types(slice(None, None, None), int, int, int)
+    assert check_types(slice(1j, 'x'), complex, str, int)
+    assert check_types(slice(None, 'x'), int, str, int)
+    assert check_types(slice(1j, None), complex, int, int)
+    assert check_types(slice(None, None), int, int, int)
+    assert check_types(slice(1j), int, complex, int)
+    assert check_types(slice(None), int, int, int)
+
+    # eq / ne
+    assert slice(1, 2, 3) == slice(1, 2, 3)
+    assert slice(0, 2, 3) != slice(1, 2, 3)
+    assert slice(1, 0, 3) != slice(1, 2, 3)
+    assert slice(1, 2, 0) != slice(1, 2, 3)
+    assert slice(None, None, None) == slice(None, None, None)
+    assert slice(None, 42, None) == slice(None, 42, None)
+    assert slice(None, 42, None) != slice(None, 43, None)
+    assert slice(1, None, 3) == slice(1, None, 3)
+    assert slice(1, None, 3) != slice(1, None, 0)
+    assert slice(1, None, 3) != slice(0, None, 3)
+    assert slice(1) == slice(1)
+    assert slice(1) != slice(2)
 test_slice()
 
 @test