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/Tests/Span.cpp

@@ -0,0 +1,126 @@
+/*
+ * 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.
+ */
+
+#include <AK/TestSuite.h>
+
+#include <AK/Checked.h>
+#include <AK/Span.h>
+#include <AK/StdLibExtras.h>
+
+TEST_CASE(default_constructor_is_empty)
+{
+    Span<int> span;
+    EXPECT(span.is_empty());
+}
+
+TEST_CASE(span_works_with_constant_types)
+{
+    const u8 buffer[4] { 1, 2, 3, 4 };
+    ReadonlyBytes bytes { buffer, 4 };
+
+    EXPECT(AK::IsConst<AK::RemoveReference<decltype(bytes[1])>::Type>::value);
+    EXPECT_EQ(bytes[2], 3);
+}
+
+TEST_CASE(span_works_with_mutable_types)
+{
+    u8 buffer[4] { 1, 2, 3, 4 };
+    Bytes bytes { buffer, 4 };
+
+    EXPECT_EQ(bytes[2], 3);
+    ++bytes[2];
+    EXPECT_EQ(bytes[2], 4);
+}
+
+TEST_CASE(iterator_behaves_like_loop)
+{
+    u8 buffer[256];
+    for (int idx = 0; idx < 256; ++idx) {
+        buffer[idx] = static_cast<u8>(idx);
+    }
+
+    Bytes bytes { buffer, 256 };
+    size_t idx = 0;
+    for (auto iter = bytes.begin(); iter < bytes.end(); ++iter) {
+        EXPECT_EQ(*iter, buffer[idx]);
+
+        ++idx;
+    }
+}
+
+TEST_CASE(modifying_is_possible)
+{
+    int values_before[8] = { 1, 2, 3, 4, 5, 6, 7, 8 };
+    int values_after[8] = { 7, 6, 5, 4, 3, 2, 1, 0 };
+
+    Span<int> span { values_before, 8 };
+    for (auto& value : span) {
+        value = 8 - value;
+    }
+
+    for (int idx = 0; idx < 8; ++idx) {
+        EXPECT_EQ(values_before[idx], values_after[idx]);
+    }
+}
+
+TEST_CASE(at_and_index_operator_return_same_value)
+{
+    u8 buffer[256];
+    for (int idx = 0; idx < 256; ++idx) {
+        buffer[idx] = static_cast<u8>(idx);
+    }
+
+    Bytes bytes { buffer, 256 };
+    for (int idx = 0; idx < 256; ++idx) {
+        EXPECT_EQ(buffer[idx], bytes[idx]);
+        EXPECT_EQ(bytes[idx], bytes.at(idx));
+    }
+}
+
+TEST_CASE(can_subspan_whole_span)
+{
+    u8 buffer[16];
+    Bytes bytes { buffer, 16 };
+
+    Bytes subspan = bytes.subspan(0, 16);
+
+    EXPECT_EQ(subspan.data(), buffer);
+    EXPECT_EQ(subspan.size(), 16u);
+}
+
+TEST_CASE(can_subspan_as_intended)
+{
+    const u16 buffer[8] { 1, 2, 3, 4, 5, 6, 7, 8 };
+
+    Span<const u16> span { buffer, 8 };
+    auto subspan = span.subspan(3, 2);
+
+    EXPECT_EQ(subspan.size(), 2u);
+    EXPECT_EQ(subspan[0], 4);
+    EXPECT_EQ(subspan[1], 5);
+}
+
+TEST_MAIN(Span)