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Extension System

NUClear's DSL is fully extensible. Every built-in word — Trigger, With, Every, Pool — is implemented using the same extension mechanism available to you. Custom DSL words are first-class citizens.

How It Works

A DSL word is a struct that implements one or more static template methods called extension points. When you write an on<>() statement combining multiple words, the Fusion Engine introspects each word, discovers which extension points it provides, and combines them into a single fused reaction.

// A DSL word is just a struct with static methods
struct MyWord {
    template <typename DSL>
    static void bind(const std::shared_ptr<threading::Reaction>& reaction) {
        // Called when the reaction is created
    }

    template <typename DSL>
    static Data get(threading::ReactionTask& task) {
        // Called when the reaction runs — provides data to the callback
    }
};

flowchart LR
    U["on&lt;Custom, Trigger&lt;T&gt;&gt;()"] --> F["Fusion Engine"]
    F --> B["bind: Custom::bind + Trigger::bind"]
    F --> G["get: Custom::get + Trigger::get"]
    F --> P["priority: resolved"]
    B --> R["Reaction created"]
    G --> R
    P --> R

Architecture

The extension system has several components:

  • Extension Points — The static methods a word can implement to hook into the reaction lifecycle
  • Fusion Engine — The compile-time machinery that discovers and combines extension points across words
  • Data Stores — Thread-safe and thread-local storage used to pass data between emit handlers and reaction callbacks
  • Built-in Extensions — Reactor-based controllers that provide time, IO, network, and trace functionality

In This Section

Page Description
Extension Points All available hooks and their signatures
Fusion Engine How words are combined at compile time
Data Stores Storage mechanisms for inter-component communication
Built-in Extensions The four controller reactors shipped with NUClear

See Also