Made the message queue iterable.

source/mijin/async/message_queue.hpp

@@ -25,9 +25,59 @@ namespace mijin
 // public types
 //
 
+template<typename TMessageQueue>
+class MessageQueueIterator
+{
+public:
+    using value_type = typename TMessageQueue::message_t;
+    using reference = value_type&;
+    using pointer = value_type*;
+private:
+    TMessageQueue* queue_ = nullptr;
+    std::optional<value_type> message_;
+public:
+    MessageQueueIterator() = default;
+    explicit MessageQueueIterator(TMessageQueue& queue) noexcept : queue_(&queue) {
+        message_ = queue_->tryPop();
+    }
+    MessageQueueIterator(const MessageQueueIterator&) = delete;
+    MessageQueueIterator(MessageQueueIterator&&) = default;
+
+    MessageQueueIterator& operator=(const MessageQueueIterator&) = delete;
+    MessageQueueIterator& operator=(MessageQueueIterator&&) = default;
+
+    bool operator==(const MessageQueueIterator& other) noexcept
+    {
+        return message_.has_value() == other.message_.has_value();
+    }
+    bool operator!=(const MessageQueueIterator& other) noexcept
+    {
+        return !(*this == other);
+    }
+
+    reference operator*() noexcept
+    {
+        return message_.value();
+    }
+
+    pointer operator->() noexcept
+    {
+        return &message_.value();
+    }
+
+    MessageQueueIterator& operator++() noexcept
+    {
+        message_ = queue_->tryPop();
+        return *this;
+    }
+};
+
 template<typename TMessage, std::size_t bufferSize = 32>
 class MessageQueue
 {
+public:
+    using message_t = TMessage;
+    using iterator_t = MessageQueueIterator<MessageQueue<TMessage, bufferSize>>;
 private:
     std::array<TMessage, bufferSize> messages;
     mijin::BitArray<bufferSize, true> messageReady;
@@ -48,6 +98,9 @@ public:
     void push(TMessage message);
     [[nodiscard]] std::optional<TMessage> tryPop();
     [[nodiscard]] TMessage wait();
+
+    iterator_t begin() noexcept { return iterator_t(*this); }
+    iterator_t end() noexcept { return iterator_t(); }
 };
 
 template<typename TRequest, typename TResponse, std::size_t requestBufferSize = 32, std::size_t responseBufferSize = 32>