split.cpp

teplate <class T>
auto split(future<T>&&) -> pair<future<T>, future<T>>;

// Q: Is the only way to attach a continuation to spawn/await?

class application {
  //...
  future<document> _document;
  vector<future<void>> _pending; // async scope
  
  // implementation of save with split - not const
  void save() { 
    auto [f1, f2] split(_document);
    _document = move(f1); // requires save is mutable - copy would not
    _pending.push_back(spawn([_f = move(f2)] {
        _f.await().save();
    });           
  }
  
  // implementation of save with copy
  void save() const { 
    _pending.push_back(spawn([_f = copy(_document)] {
        _f.await().save();
    });
  }
                       
  // implementation of save with continuations - stlab syntax
  void save() const {
    _pending.push_back(copy(_document) | [](const document& d){
      d.save();
    });
  }
  
  void blur() {
    _document = spawn([_f = move(_document)]{
      _f.await().blur();
    });
  }
                       
};

application _application;

int main() {
  while (true) { // run loop
    char command;
    cin >> command;
    switch (command) {
      case 's': _application.save(); break;
      case 'b': _application.blur(); break;
      default: break; // do nothing
    }
  }
  
}