Source/bmalloc/bmalloc/List.h

/*
 * Copyright (C) 2016 Apple Inc. 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 APPLE INC. ``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 APPLE INC. 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. 
 */

#ifndef List_h
#define List_h

namespace bmalloc {

template<typename T>
struct ListNode {
    ListNode<T>* prev { nullptr };
    ListNode<T>* next { nullptr };
};

template<typename T>
class List {
    static_assert(std::is_trivially_destructible<T>::value, "List must have a trivial destructor.");

    struct iterator {
        T* operator*() { return static_cast<T*>(m_node); }
        T* operator->() { return static_cast<T*>(m_node); }

        bool operator!=(const iterator& other) { return m_node != other.m_node; }

        iterator& operator++()
        {
            m_node = m_node->next;
            return *this;
        }
        
        ListNode<T>* m_node { nullptr };
    };

public:
    List() { }

    bool isEmpty() { return m_root.next == &m_root; }

    T* head() { return static_cast<T*>(m_root.next); }
    T* tail() { return static_cast<T*>(m_root.prev); }
    
    iterator begin() { return iterator { m_root.next }; }
    iterator end() { return iterator { &m_root }; }

    void push(T* node)
    {
        ListNode<T>* it = tail();
        insertAfter(it, node);
    }

    void pushFront(T* node)
    {
        ListNode<T>* it = &m_root;
        insertAfter(it, node);
    }

    T* pop()
    {
        ListNode<T>* result = tail();
        remove(result);
        return static_cast<T*>(result);
    }

    T* popFront()
    {
        ListNode<T>* result = head();
        remove(result);
        return static_cast<T*>(result);
    }

    static void insertAfter(ListNode<T>* it, ListNode<T>* node)
    {
        ListNode<T>* prev = it;
        ListNode<T>* next = it->next;

        node->next = next;
        next->prev = node;

        node->prev = prev;
        prev->next = node;
    }

    static void remove(ListNode<T>* node)
    {
        ListNode<T>* next = node->next;
        ListNode<T>* prev = node->prev;

        next->prev = prev;
        prev->next = next;
        
        node->prev = nullptr;
        node->next = nullptr;
    }

private:
    ListNode<T> m_root { &m_root, &m_root };
};

} // namespace bmalloc

#endif // List_h