AK: Implement Span which represents a contiguous sequence of objects.

This makes it possible to pass one object rather than pointer and length
individually.

AK/Span.h

@@ -0,0 +1,130 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * 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 {
+
+template<typename T>
+class Span {
+public:
+    using Iterator = T*;
+    using ConstIterator = const T*;
+
+    static_assert(!IsPointer<T>::value);
+
+    ALWAYS_INLINE Span() = default;
+    ALWAYS_INLINE Span(T* values, size_t size)
+        : m_values(values)
+        , m_size(size)
+    {
+        ASSERT(!Checked<uintptr_t>::addition_would_overflow((uintptr_t)values, size * sizeof(T)));
+    }
+    ALWAYS_INLINE Span(const Span& other)
+        : m_values(other.m_values)
+        , m_size(other.m_size)
+    {
+    }
+    ALWAYS_INLINE Span(const Span<RemoveConst<T>>& other)
+        : m_values(other.m_values)
+        , m_size(other.m_size)
+    {
+    }
+
+    ALWAYS_INLINE const T* data() const { return m_values; }
+    ALWAYS_INLINE T* data() { return m_values; }
+
+    ALWAYS_INLINE ConstIterator begin() const
+    {
+        return m_values;
+    }
+    ALWAYS_INLINE ConstIterator end() const
+    {
+        return begin() + m_size;
+    }
+
+    ALWAYS_INLINE Iterator begin()
+    {
+        return m_values;
+    }
+    ALWAYS_INLINE Iterator end()
+    {
+        return begin() + m_size;
+    }
+
+    ALWAYS_INLINE size_t size() const { return m_size; }
+
+    ALWAYS_INLINE bool is_empty() const { return m_size == 0; }
+
+    ALWAYS_INLINE Span<T> subspan(size_t start, size_t size) const
+    {
+        ASSERT(start + size <= m_size);
+        return { m_values + start, size };
+    }
+
+    ALWAYS_INLINE const T& at(size_t index) const
+    {
+        ASSERT(index < m_size);
+        return m_values[index];
+    }
+    ALWAYS_INLINE T& at(size_t index)
+    {
+        ASSERT(index < m_size);
+        return m_values[index];
+    }
+
+    ALWAYS_INLINE T& operator[](size_t index) const
+    {
+        return m_values[index];
+    }
+    ALWAYS_INLINE T& operator[](size_t index)
+    {
+        return m_values[index];
+    }
+
+    ALWAYS_INLINE T& operator=(const T& other)
+    {
+        m_size = other.m_size;
+        m_values = other.m_values;
+    }
+
+protected:
+    T* m_values { nullptr };
+    size_t m_size { 0 };
+};
+
+using ReadonlyBytes = Span<const u8>;
+using Bytes = Span<u8>;
+
+}
+
+using AK::Bytes;
+using AK::ReadonlyBytes;
+using AK::Span;