AK: Add a FixedArray<T> container

This is a simple array wrapper that knows its size. It has begin/end
so you can use range-for. It also has a resize() that reallocates.

3 files changed, 144 insertions, 3 deletions

diff --git a/AK/FixedArray.h b/AK/FixedArray.h
new file mode 100644
index 0000000000..cfe3eb3fae
--- /dev/null
+++ b/AK/FixedArray.h
@@ -0,0 +1,83 @@
+#pragma once
+
+#include <AK/Vector.h>
+
+namespace AK {
+
+template<typename T>
+class FixedArray {
+public:
+    FixedArray() {}
+    explicit FixedArray(size_t size)
+        : m_size(size)
+    {
+        m_elements = (T*)kmalloc(sizeof(T) * m_size);
+        for (size_t i = 0; i < m_size; ++i)
+            new (&m_elements[i]) T();
+    }
+    ~FixedArray()
+    {
+        clear();
+    }
+
+    FixedArray(const FixedArray& other)
+        : m_size(other.m_size)
+    {
+        m_elements = (T*)kmalloc(sizeof(T) * m_size);
+        for (size_t i = 0; i < m_size; ++i)
+            new (&m_elements[i]) T(other[i]);
+    }
+
+    FixedArray& operator=(const FixedArray&) = delete;
+    FixedArray(FixedArray&&) = delete;
+    FixedArray& operator=(FixedArray&&) = delete;
+
+    void clear()
+    {
+        if (!m_elements)
+            return;
+        for (size_t i = 0; i < m_size; ++i)
+            m_elements[i].~T();
+        kfree(m_elements);
+        m_elements = nullptr;
+        m_size = 0;
+    }
+
+    size_t size() const { return m_size; }
+
+    T& operator[](size_t index) { return m_elements[index]; }
+    const T& operator[](size_t index) const { return m_elements[index]; }
+
+    void resize(size_t new_size)
+    {
+        if (new_size == m_size)
+            return;
+        auto* new_elements = (T*)kmalloc(new_size * sizeof(T));
+        for (size_t i = 0; i < min(new_size, m_size); ++i)
+            new (&new_elements[i]) T(move(m_elements[i]));
+        for (size_t i = min(new_size, m_size); i < new_size; ++i)
+            new (&new_elements[i]) T();
+        for (size_t i = 0; i < m_size; ++i)
+            m_elements[i].~T();
+        if (m_elements)
+            kfree(m_elements);
+        m_elements = new_elements;
+        m_size = new_size;
+    }
+
+    using Iterator = VectorIterator<FixedArray, T>;
+    Iterator begin() { return Iterator(*this, 0); }
+    Iterator end() { return Iterator(*this, size()); }
+
+    using ConstIterator = VectorIterator<const FixedArray, const T>;
+    ConstIterator begin() const { return ConstIterator(*this, 0); }
+    ConstIterator end() const { return ConstIterator(*this, size()); }
+
+private:
+    size_t m_size { 0 };
+    T* m_elements { nullptr };
+};
+
+}
+
+using AK::FixedArray;
diff --git a/AK/Tests/Makefile b/AK/Tests/Makefile
index 30e940dc3a..7621cf97bb 100644
--- a/AK/Tests/Makefile
+++ b/AK/Tests/Makefile
@@ -1,4 +1,4 @@
-PROGRAMS = TestString TestQueue TestVector TestHashMap TestJSON TestWeakPtr TestNonnullRefPtr TestRefPtr
+PROGRAMS = TestString TestQueue TestVector TestHashMap TestJSON TestWeakPtr TestNonnullRefPtr TestRefPtr TestFixedArray
 
 CXXFLAGS = -std=c++17 -Wall -Wextra -ggdb3 -O2 -I../ -I../../
 
@@ -32,10 +32,13 @@ TestQueue: TestQueue.o $(SHARED_TEST_OBJS)
 
 TestVector: TestVector.o $(SHARED_TEST_OBJS)
 	$(PRE_CXX) $(CXX) $(CXXFLAGS) -o $@ TestVector.o $(SHARED_TEST_OBJS)
-#
+
+TestFixedArray: TestFixedArray.o $(SHARED_TEST_OBJS)
+	$(PRE_CXX) $(CXX) $(CXXFLAGS) -o $@ TestFixedArray.o $(SHARED_TEST_OBJS)
+
 TestHashMap: TestHashMap.o $(SHARED_TEST_OBJS)
 	$(PRE_CXX) $(CXX) $(CXXFLAGS) -o $@ TestHashMap.o $(SHARED_TEST_OBJS)
-#
+
 TestJSON: TestJSON.o $(SHARED_TEST_OBJS)
 	$(PRE_CXX) $(CXX) $(CXXFLAGS) -o $@ TestJSON.o $(SHARED_TEST_OBJS)
 
diff --git a/AK/Tests/TestFixedArray.cpp b/AK/Tests/TestFixedArray.cpp
new file mode 100644
index 0000000000..92fe01b24c
--- /dev/null
+++ b/AK/Tests/TestFixedArray.cpp
@@ -0,0 +1,55 @@
+#include <AK/TestSuite.h>
+
+#include <AK/AKString.h>
+#include <AK/FixedArray.h>
+
+TEST_CASE(construct)
+{
+    EXPECT(FixedArray<int>().size() == 0);
+}
+
+TEST_CASE(ints)
+{
+    FixedArray<int> ints(3);
+    ints[0] = 0;
+    ints[1] = 1;
+    ints[2] = 2;
+    EXPECT_EQ(ints[0], 0);
+    EXPECT_EQ(ints[1], 1);
+    EXPECT_EQ(ints[2], 2);
+
+    ints.clear();
+    EXPECT_EQ(ints.size(), 0u);
+}
+
+TEST_CASE(resize)
+{
+    FixedArray<String> strings(2);
+    strings[0] = "ABC";
+    strings[1] = "DEF";
+
+    EXPECT_EQ(strings.size(), 2u);
+    EXPECT_EQ(strings[0], "ABC");
+    EXPECT_EQ(strings[1], "DEF");
+
+    strings.resize(4);
+
+    EXPECT_EQ(strings.size(), 4u);
+    EXPECT_EQ(strings[0], "ABC");
+    EXPECT_EQ(strings[1], "DEF");
+
+    EXPECT_EQ(strings[2].is_null(), true);
+    EXPECT_EQ(strings[3].is_null(), true);
+
+    strings[2] = "GHI";
+    strings[3] = "JKL";
+
+    EXPECT_EQ(strings[2], "GHI");
+    EXPECT_EQ(strings[3], "JKL");
+
+    strings.resize(1);
+    EXPECT_EQ(strings.size(), 1u);
+    EXPECT_EQ(strings[0], "ABC");
+}
+
+TEST_MAIN(FixedArray)