generator

include/utl/generator.h

@@ -0,0 +1,58 @@
+#include <coroutine>
+#include <exception>
+
+namespace utl {
+
+template <typename T>
+struct generator {
+  struct promise_type {
+    generator get_return_object() { return handle_type::from_promise(*this); }
+    std::suspend_always initial_suspend() { return {}; }
+    std::suspend_always final_suspend() noexcept { return {}; }
+    void unhandled_exception() { exception_ = std::current_exception(); }
+
+    template <std::convertible_to<T> From>
+    std::suspend_always yield_value(From&& from) {
+      value_ = std::forward<From>(from);
+      return {};
+    }
+
+    void return_void() {}
+
+    T value_;
+    std::exception_ptr exception_;
+  };
+
+  using handle_type = std::coroutine_handle<promise_type>;
+
+  generator(handle_type h) : h_(h) {}
+
+  ~generator() { h_.destroy(); }
+
+  explicit operator bool() {
+    fill();
+    return !h_.done();
+  }
+
+  T operator()() {
+    fill();
+    full_ = false;
+    return std::move(h_.promise().value_);
+  }
+
+private:
+  void fill() {
+    if (!full_) {
+      h_();
+      if (h_.promise().exception_) {
+        std::rethrow_exception(h_.promise().exception_);
+      }
+      full_ = true;
+    }
+  }
+
+  handle_type h_;
+  bool full_{false};
+};
+
+}  // namespace utl