PositionManager (concept / trait / ref)

Compile-time contract and type-erased handle for components that track per-symbol positions based on order-execution events.

// Concept
template <typename T>
concept PositionManager =
    OrderExecutionListener<T> && Subsystem<T> &&
    requires(T pm, SymbolId sym) {
      { pm.getPosition(sym) } -> std::same_as<Quantity>;
    };

Piece	Responsibility
PositionManagerTrait	Builds a static v-table by extending OrderExecutionListenerTrait with getPosition().
PositionManagerRef	Two-pointer handle {void*, VTable*} that forwards order callbacks and position queries without virtuals.

PositionManagerRef API

// Lifecycle & subscription (inherited)
SubscriberId   id()   const;
SubscriberMode mode() const;
void start() const;
void stop()  const;

// Order-execution fan-out (inherited)
void onOrderSubmitted     (const Order&)           const;
void onOrderAccepted      (const Order&)           const;
void onOrderPartiallyFilled(const Order&, Quantity)const;
void onOrderFilled        (const Order&)           const;
void onOrderCanceled      (const Order&)           const;
void onOrderExpired       (const Order&)           const;
void onOrderRejected      (const Order&, const std::string&) const;
void onOrderReplaced      (const Order&, const Order&) const;

// Position query
Quantity getPosition(SymbolId) const;

Purpose

• Maintain real-time net position per symbol for PnL, risk checks, and strategy decisions.
• React to every order update through the inherited OrderExecutionListener interface, updating internal position state.

Notes

• Zero runtime overhead beyond one pointer indirection per call.
• Implementers just need to satisfy concepts::PositionManager; no runtime registration required.