Use __index__ for __getitem__ and __setitem__

When indexing stdlib containers we should accept a generic type that calls
on the  __index__ method to allow types other than Int to be used but
doesn't allow Intable types that should not be used for such purposes
(such as Float)

Signed-off-by: Brian Grenier <grenierb96@gmail.com>

stdlib/src/builtin/bool.mojo

@@ -57,7 +57,12 @@ trait Boolable:
 @value
 @register_passable("trivial")
 struct Bool(
-    Stringable, CollectionElement, Boolable, EqualityComparable, Intable
+    Stringable,
+    CollectionElement,
+    Boolable,
+    EqualityComparable,
+    Intable,
+    Indexer,
 ):
     """The primitive Bool scalar value used in Mojo."""
 
@@ -299,10 +304,18 @@ struct Bool(
         """
         return lhs ^ self
 
+    # ===----------------------------------------------------------------------=== #
+    #  bool
+    # ===----------------------------------------------------------------------=== #
 
-# ===----------------------------------------------------------------------=== #
-#  bool
-# ===----------------------------------------------------------------------=== #
+    @always_inline("nodebug")
+    fn __index__(self) -> Int:
+        """Convert this Bool to an integer for indexing purposes
+
+        Returns:
+            Bool as Int
+        """
+        return self.__int__()
 
 
 @always_inline

stdlib/src/builtin/builtin_list.mojo

@@ -138,16 +138,19 @@ struct VariadicList[type: AnyRegType](Sized):
         return __mlir_op.`pop.variadic.size`(self.value)
 
     @always_inline
-    fn __getitem__(self, index: Int) -> type:
+    fn __getitem__[indexer: Indexer](self, idx: indexer) -> type:
         """Gets a single element on the variadic list.
 
+        Parameters:
+            indexer: The type of the indexing value.
+
         Args:
-            index: The index of the element to access on the list.
+            idx: The index of the element to access on the list.
 
         Returns:
             The element on the list corresponding to the given index.
         """
-        return __mlir_op.`pop.variadic.get`(self.value, index.value)
+        return __mlir_op.`pop.variadic.get`(self.value, index(idx).value)
 
     @always_inline
     fn __iter__(self) -> Self.IterType:
@@ -344,18 +347,21 @@ struct VariadicListMem[
     # TODO: Fix for loops + _VariadicListIter to support a __nextref__ protocol
     # allowing us to get rid of this and make foreach iteration clean.
     @always_inline
-    fn __getitem__(self, index: Int) -> Self.reference_type:
+    fn __getitem__[indexer: Indexer](self, idx: indexer) -> Self.reference_type:
         """Gets a single element on the variadic list.
 
+        Parameters:
+            indexer: The type of the indexing value.
+
         Args:
-            index: The index of the element to access on the list.
+            idx: The index of the element to access on the list.
 
         Returns:
             A low-level pointer to the element on the list corresponding to the
             given index.
         """
         return Self.reference_type(
-            __mlir_op.`pop.variadic.get`(self.value, index.value)
+            __mlir_op.`pop.variadic.get`(self.value, index(idx).value)
         )
 
     @always_inline

stdlib/src/builtin/builtin_slice.mojo

@@ -149,16 +149,19 @@ struct Slice(Sized, Stringable, EqualityComparable):
         return len(range(self.start, self.end, self.step))
 
     @always_inline
-    fn __getitem__(self, idx: Int) -> Int:
+    fn __getitem__[indexer: Indexer](self, idx: indexer) -> Int:
         """Get the slice index.
 
+        Parameters:
+            indexer: The type of the indexing value.
+
         Args:
             idx: The index.
 
         Returns:
             The slice index.
         """
-        return self.start + idx * self.step
+        return self.start + index(idx) * self.step
 
     @always_inline("nodebug")
     fn _has_end(self) -> Bool:

stdlib/src/builtin/int.mojo

@@ -204,6 +204,7 @@ struct Int(
     KeyElement,
     Roundable,
     Stringable,
+    Indexer,
 ):
     """This type represents an integer value."""
 

stdlib/src/builtin/int_literal.mojo

@@ -28,6 +28,7 @@ struct IntLiteral(
     Intable,
     Roundable,
     Stringable,
+    Indexer,
 ):
     """This type represents a static integer literal value with
     infinite precision.  They can't be materialized at runtime and

stdlib/src/builtin/range.mojo

@@ -82,8 +82,8 @@ struct _ZeroStartingRange(Sized, ReversibleRange):
         return self.curr
 
     @always_inline("nodebug")
-    fn __getitem__(self, idx: Int) -> Int:
-        return idx
+    fn __getitem__[indexer: Indexer](self, idx: indexer) -> Int:
+        return index(idx)
 
     @always_inline("nodebug")
     fn __reversed__(self) -> _StridedRangeIterator:
@@ -113,8 +113,8 @@ struct _SequentialRange(Sized, ReversibleRange):
         return self.end - self.start if self.start < self.end else 0
 
     @always_inline("nodebug")
-    fn __getitem__(self, idx: Int) -> Int:
-        return self.start + idx
+    fn __getitem__[indexer: Indexer](self, idx: indexer) -> Int:
+        return self.start + index(idx)
 
     @always_inline("nodebug")
     fn __reversed__(self) -> _StridedRangeIterator:
@@ -185,8 +185,8 @@ struct _StridedRange(Sized, ReversibleRange):
         return _div_ceil_positive(abs(self.start - self.end), abs(self.step))
 
     @always_inline("nodebug")
-    fn __getitem__(self, idx: Int) -> Int:
-        return self.start + idx * self.step
+    fn __getitem__[indexer: Indexer](self, idx: indexer) -> Int:
+        return self.start + index(idx) * self.step
 
     @always_inline("nodebug")
     fn __reversed__(self) -> _StridedRangeIterator:

stdlib/src/builtin/simd.mojo

@@ -132,6 +132,7 @@ struct SIMD[type: DType, size: Int = simdwidthof[type]()](
     Roundable,
     Sized,
     Stringable,
+    Indexer,
 ):
     """Represents a small vector that is backed by a hardware vector element.
 
@@ -502,6 +503,22 @@ struct SIMD[type: DType, size: Int = simdwidthof[type]()](
             rebind[Scalar[type]](self).value
         )
 
+    @always_inline("nodebug")
+    fn __index__(self) -> Int:
+        """Returns the value as an int if it is an integral value
+
+        Contraints:
+            Must be an integral value
+
+        Returns:
+            The value as an integer
+        """
+        constrained[
+            type.is_integral() or type.is_bool(),
+            "expected integral or bool type",
+        ]()
+        return self.__int__()
+
     @always_inline
     fn __str__(self) -> String:
         """Get the SIMD as a string.
@@ -1742,9 +1759,12 @@ struct SIMD[type: DType, size: Int = simdwidthof[type]()](
     # ===-------------------------------------------------------------------===#
 
     @always_inline("nodebug")
-    fn __getitem__(self, idx: Int) -> Scalar[type]:
+    fn __getitem__[indexer: Indexer](self, idx: indexer) -> Scalar[type]:
         """Gets an element from the vector.
 
+        Parameters:
+            indexer: The type of the indexing value.
+
         Args:
             idx: The element index.
 
@@ -1753,32 +1773,44 @@ struct SIMD[type: DType, size: Int = simdwidthof[type]()](
         """
         return __mlir_op.`pop.simd.extractelement`[
             _type = __mlir_type[`!pop.scalar<`, type.value, `>`]
-        ](self.value, idx.value)
+        ](self.value, index(idx).value)
 
     @always_inline("nodebug")
-    fn __setitem__(inout self, idx: Int, val: Scalar[type]):
+    fn __setitem__[
+        indexer: Indexer
+    ](inout self, idx: indexer, val: Scalar[type]):
         """Sets an element in the vector.
 
+        Parameters:
+            indexer: The type of the indexing value.
+
         Args:
             idx: The index to set.
             val: The value to set.
         """
         self.value = __mlir_op.`pop.simd.insertelement`(
-            self.value, val.value, idx.value
+            self.value, val.value, index(idx).value
         )
 
     @always_inline("nodebug")
-    fn __setitem__(
-        inout self, idx: Int, val: __mlir_type[`!pop.scalar<`, type.value, `>`]
+    fn __setitem__[
+        indexer: Indexer
+    ](
+        inout self,
+        idx: indexer,
+        val: __mlir_type[`!pop.scalar<`, type.value, `>`],
     ):
         """Sets an element in the vector.
 
+        Parameters:
+            indexer: The type of the indexing value.
+
         Args:
             idx: The index to set.
             val: The value to set.
         """
         self.value = __mlir_op.`pop.simd.insertelement`(
-            self.value, val, idx.value
+            self.value, val, index(idx).value
         )
 
     fn __hash__(self) -> Int:

stdlib/src/builtin/string.mojo

@@ -687,21 +687,25 @@ struct String(
         """
         return len(self) > 0
 
-    fn __getitem__(self, idx: Int) -> String:
+    fn __getitem__[indexer: Indexer](self, idx: indexer) -> String:
         """Gets the character at the specified position.
 
+        Parameters:
+            indexer: The type of the indexing value.
+
         Args:
             idx: The index value.
 
         Returns:
             A new string containing the character at the specified position.
         """
-        if idx < 0:
-            return self.__getitem__(len(self) + idx)
+        var index_val = index(idx)
+        if index_val < 0:
+            return self.__getitem__(len(self) + index_val)
 
-        debug_assert(0 <= idx < len(self), "index must be in range")
+        debug_assert(0 <= index_val < len(self), "index must be in range")
         var buf = Self._buffer_type(capacity=1)
-        buf.append(self._buffer[idx])
+        buf.append(self._buffer[index_val])
         buf.append(0)
         return String(buf^)
 

stdlib/src/builtin/value.mojo

@@ -145,3 +145,26 @@ trait RepresentableCollectionElement(CollectionElement, Representable):
     """
 
     pass
+
+
+trait Indexer:
+    """This trait denotes a type that can be used to index a container that
+    handles integral index values.
+
+    This solves the issue of being able to index data structures such as `List` with the various
+    integral types without being too broad and allowing types that should not be used such as float point
+    values.
+    """
+
+    fn __index__(self) -> Int:
+        """Return the index value
+
+        Returns:
+            The index value of the object
+        """
+        ...
+
+
+@always_inline("nodebug")
+fn index[indexer: Indexer](idx: indexer) -> Int:
+    return idx.__index__()