broadcaster.hh

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// SPDX-FileCopyrightText: 2021-2025 The Ikarus Developers mueller@ibb.uni-stuttgart.de
// SPDX-License-Identifier: LGPL-3.0-or-later
 
#pragma once
#include <functional>
#include <memory>
#include <vector>
 
namespace Ikarus {
 
template <class Args>
struct Broadcaster;
 
template <typename... Args>
class Broadcaster<void(Args...)>
{
  using F = std::function<void(Args...)>;
 
  // The functions are stored as weak pointer, therefore the Broadcaster has no ownership over them.
  std::vector<std::weak_ptr<F>> listeners;
 
public:
  using Token = std::shared_ptr<F>;
 
  Token registerListener(F f) {
    auto sp = std::make_shared<F>(std::move(f));
    listeners.push_back(sp);
    return sp;
  }
 
  // Unregister a listener
  void unregisterListener(Token&& t) { t = nullptr; }
 
  void notify(Args... args) {
    trim();
    for (auto& w : listeners) {
      if (auto p = w.lock()) {
        (*p)(args...);
      }
    }
  }
 
private:
  // Remove expired listeners, we need that because the weak pointers could already be invalidated (i.e. refcount == 0).
  void trim() {
    listeners.erase(std::remove_if(listeners.begin(), listeners.end(), [](auto& p) { return p.expired(); }),
                    listeners.end());
  }
};
 
template <typename... Signatures>
class Broadcasters : public Broadcaster<Signatures>...
{
public:
  using Broadcaster<Signatures>::registerListener...;
  using Broadcaster<Signatures>::unregisterListener...;
  using Broadcaster<Signatures>::notify...;
 
  // Access a specific broadcaster for a given message type
  template <typename M>
  Broadcaster<M>& station() {
    return *this;
  }
 
  // Access a specific broadcaster for a given message type (const version)
  template <typename M>
  const Broadcaster<M>& station() const {
    return *this;
  }
};
 
} // namespace Ikarus