Add BytesView

This is a 1:1 clone of VecView

builtin/builtin.mbti

@@ -123,6 +123,15 @@ impl Buffer {
   write_sub_string(Self, String, Int, Int) -> Unit
 }
 
+type BytesView
+impl BytesView {
+  length(Self) -> Int
+  op_as_view(Self, ~start : Int, ~end : Int) -> Self
+  op_get(Self, Int) -> Byte
+  op_set(Self, Int, Byte) -> Unit
+  swap(Self, Int, Int) -> Unit
+}
+
 type Iter
 impl Iter {
   _unstable_internal_make[T](((T) -> Bool) -> Bool) -> Self[T]
@@ -343,6 +352,7 @@ impl Bytes {
   length(Bytes) -> Int
   make(Int, ~init : Byte = ..) -> Bytes
   of_string(String) -> Bytes
+  op_as_view(Bytes, ~start : Int, ~end : Int) -> BytesView
   op_get(Bytes, Int) -> Byte
   op_set(Bytes, Int, Byte) -> Unit
   set_utf16_char(Bytes, Int, Char) -> Int

builtin/bytesview.mbt

@@ -0,0 +1,78 @@
+// Copyright 2024 International Digital Economy Academy
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/// A `BytesView` is a slice of a `Bytes`.
+struct BytesView {
+  buf : Bytes
+  start : Int
+  len : Int
+}
+
+pub fn length(self : BytesView) -> Int {
+  self.len
+}
+
+pub fn op_get(self : BytesView, index : Int) -> Byte {
+  if index < 0 || index >= self.len {
+    let len = self.len
+    abort(
+      "index out of bounds: the len is from 0 to \(len) but the index is \(index)",
+    )
+  }
+  self.buf[self.start + index]
+}
+
+pub fn op_set(self : BytesView, index : Int, value : Byte) -> Unit {
+  if index < 0 || index >= self.len {
+    let len = self.len
+    abort(
+      "index out of bounds: the len is from 0 to \(len) but the index is \(index)",
+    )
+  }
+  self.buf[self.start + index] = value
+}
+
+pub fn swap(self : BytesView, i : Int, j : Int) -> Unit {
+  if i >= self.len || j >= self.len || i < 0 || j < 0 {
+    let len = self.len
+    abort(
+      "index out of bounds: the len is from 0 to \(len) but the index is (\(i), \(j))",
+    )
+  }
+  let temp = self.buf[self.start + i]
+  self.buf[self.start + i] = self.buf[self.start + j]
+  self.buf[self.start + j] = temp
+}
+
+pub fn op_as_view(self : Bytes, ~start : Int, ~end : Int) -> BytesView {
+  if start < 0 {
+    abort("Slice start index out of bounds")
+  } else if end > self.length() {
+    abort("Slice end index out of bounds")
+  } else if start > end {
+    abort("Slice start index greater than end index")
+  }
+  BytesView::{ buf: self, start, len: end - start }
+}
+
+pub fn op_as_view(self : BytesView, ~start : Int, ~end : Int) -> BytesView {
+  if start < 0 {
+    abort("Slice start index out of bounds")
+  } else if end > self.len {
+    abort("Slice end index out of bounds")
+  } else if start > end {
+    abort("Slice start index greater than end index")
+  }
+  BytesView::{ buf: self.buf, start: self.start + start, len: end - start }
+}