OrderValidator (concept / trait / ref)

Compile-time contract and type-erased handle for components that validate orders before submission.

// Concept
template <typename T>
concept OrderValidator =
    requires(T v, const Order& o, std::string& r) {
      { v.validate(o, r) } -> std::same_as<bool>;
    };

Piece	Responsibility
OrderValidatorTrait	Builds a static v-table exposing a single validate method via meta::wrap.
OrderValidatorRef	Two-pointer handle {void*, VTable*} forwarding the call without virtual inheritance.

OrderValidatorRef API

bool validate(const Order& order, std::string& reason) const;

Returns true when the order passes all checks; otherwise false and sets reason.

Purpose

• Enforce pre-trade risk rules (price bands, size limits, account balance, etc.).
• Decouple validation logic from order generators and executors while keeping zero overhead (one pointer indirection).