Class Promise

src/fl/task/promise.h:58–210

/// This is a lightweight wrapper around a shared PromiseImpl for easy copying/sharing
template<typename T>
class Promise {
public:
    /// Create a pending Promise
    static Promise<T> create() FL_NOEXCEPT {
        auto impl = fl::make_shared<detail::PromiseImpl<T>>();
        return Promise<T>(impl);
    }

    /// Create a resolved Promise with value
    static Promise<T> resolve(const T& value) FL_NOEXCEPT {  // okay static in header
        auto p = create();
        p.complete_with_value(value);
        return p;
    }

    /// Create a resolved Promise with value (move version)
    static Promise<T> resolve(T&& value) FL_NOEXCEPT {  // okay static in header
        auto p = create();
        p.complete_with_value(fl::move(value));
        return p;
    }

    /// Create a rejected Promise with error
    static Promise<T> reject(const Error& error) FL_NOEXCEPT {  // okay static in header
        auto p = create();
        p.complete_with_error(error);
        return p;
    }

    /// Create a rejected Promise with error message
    static Promise<T> reject(const fl::string& error_message) FL_NOEXCEPT {  // okay static in header
        return reject(Error(error_message));
    }

    /// Default constructor - creates invalid Promise
    Promise() FL_NOEXCEPT : mImpl(nullptr) {}

    /// Copy constructor (promises are now copyable via shared implementation)
    Promise(const Promise& other) = default;

    /// Move constructor
    Promise(Promise&& other) FL_NOEXCEPT = default;

    /// Copy assignment operator
    Promise& operator=(const Promise& other) = default;

    /// Move assignment operator
    Promise& operator=(Promise&& other) FL_NOEXCEPT = default;

    /// Check if Promise is valid
    bool valid() const FL_NOEXCEPT {
        return mImpl != nullptr;
    }

    /// Register success callback - returns reference for chaining
    /// @param callback Function to call when Promise resolves successfully
    /// @returns Reference to this Promise for chaining
    Promise& then(fl::function<void(const T&)> callback) FL_NOEXCEPT {