Engine / EngineBuilder Concepts

The header defines two C++20 concepts used to enforce type-safety around engine composition.

namespace flox::concepts {

template <typename T>
concept Engine = Subsystem<T>;               // any type satisfying Subsystem

template <typename T>
concept EngineBuilder = requires(T b) {      // must expose build()
  { b.build() } -> Engine;
};

} // namespace flox::concepts

Purpose

• Engine – shorthand to require that a type fulfils the broader Subsystem concept (start/stop, etc.).
• EngineBuilder – constrains factory objects that produce an Engine via build().

Usage Example

struct MyEngine : /* implements SubsystemTrait */ { /* … */ };

struct MyBuilder {
  MyEngine build() { return MyEngine{ /* cfg */ }; }
};

static_assert(flox::concepts::Engine<MyEngine>);
static_assert(flox::concepts::EngineBuilder<MyBuilder>);

Notes

• By chaining concepts, compile-time errors point exactly to missing Subsystem requirements or absent build() methods.