get

Called during task creation to retrieve data for the user's callback. The return value becomes one of the callback arguments.

Signature

template <typename DSL>
static T get(threading::ReactionTask& task)

Details

Aspect	Detail
When	After preconditions pass, during task creation
Thread	The emitter's thread (the thread that called emit())
Returns	Data of any type — becomes a callback parameter
Fusion	Each word's return is concatenated into a flattened tuple. The tuple elements are matched to callback parameters via greedy argument matching.

Context & Arguments

• task — the ReactionTask being constructed. Provides access to the parent Reaction, the current cause (which reaction/task triggered this emit), and task metadata.

The get function runs on the emitter's thread — the thread that called emit(). This is important: if your get reads from ThreadStore, it will see the data that the emitter set. If it reads from DataStore, it gets the global latest value.

If get returns nullptr (for a pointer/shared_ptr type), the task is dropped with status MISSING_DATA — unless the word is wrapped in Optional, which converts the null to a valid empty state.

Example

struct With {
    template <typename DSL>
    static std::shared_ptr<const T> get(threading::ReactionTask& /*task*/) {
        // Return the latest value from the global data store
        return store::DataStore<T>::get();
    }
};

struct Trigger {
    template <typename DSL>
    static std::shared_ptr<const T> get(threading::ReactionTask& /*task*/) {
        // Return the data from the current emit (thread-local)
        auto* ptr = store::ThreadStore<std::shared_ptr<T>>::value;
        if (ptr != nullptr) { return *ptr; }
        // Fall back to global store
        return store::DataStore<T>::get();
    }
};

Built-in Words Using get

• Trigger<T> — reads from ThreadStore (triggering data), falls back to DataStore
• With<T> — reads from DataStore (latest value)
• Last<N, T> — returns a list of the last N triggered values
• Network<T> — deserialises the received bytes into T
• IO — returns the IO::Event struct (fd + event flags)