AK: Add a very basic Utf32View class

This allows you to wrap a { const u32* codepoints, size_t length } in a
simple object.

AK/Forward.h

@@ -46,6 +46,7 @@ class StringImpl;
 class StringView;
 class URL;
 class FlyString;
+class Utf32View;
 class Utf8View;
 
 template<typename T>
@@ -116,6 +117,7 @@ using AK::CircularQueue;
 using AK::DebugLogStream;
 using AK::DoublyLinkedList;
 using AK::FixedArray;
+using AK::FlyString;
 using AK::Function;
 using AK::HashMap;
 using AK::HashTable;
@@ -138,6 +140,6 @@ using AK::StringImpl;
 using AK::StringView;
 using AK::Traits;
 using AK::URL;
-using AK::FlyString;
+using AK::Utf32View;
 using AK::Utf8View;
 using AK::Vector;

AK/Utf32View.h

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Assertions.h>
+#include <AK/Checked.h>
+#include <AK/Types.h>
+
+namespace AK {
+
+class Utf32View {
+public:
+    Utf32View(const u32* codepoints, size_t length)
+        : m_codepoints(codepoints)
+        , m_length(length)
+    {
+    }
+
+    const u32* codepoints() const { return m_codepoints; }
+    bool is_empty() const { return m_length == 0; }
+    size_t length() const { return m_length; }
+
+    Utf32View substring_view(size_t offset, size_t length) const
+    {
+        ASSERT(offset < m_length);
+        ASSERT(!Checked<size_t>::addition_would_overflow(offset, length));
+        ASSERT((offset + length) <= m_length);
+        return Utf32View(m_codepoints + offset, length);
+    }
+
+private:
+    const u32* m_codepoints { nullptr };
+    size_t m_length { 0 };
+};
+
+}
+
+using AK::Utf32View;