class std::hash< ara::core::Optional< T > >

The template specialization std::hash<ara::core::Optional<T>> enables the computation of hash values for optional values for use in associative hash containers of the C++ Standard Library [SWS_CORE_01199]. The invocation takes place via operator operator(), which accepts a const reference to ara::core::Optional<T> and determines a hash value of type size_t [SWS_CORE_01199]. Interpretation: Depending on whether the optional contains a value, the computation is likely to either delegate to the hash functor of T or return a fixed hash value for empty instances. Question Q-f126709f8c243c75 (open) As a central constraint, the interface guarantees full exception safety through a strict noexcept specification.

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Context

The template specialization std::hash<ara::core::Optional<T>> extends the C++ Standard Library with support for the optional container type of the AUTOSAR Adaptive Platform [SWS_CORE_01199]. It acts as a standard-compliant function object that maps instances of ara::core::Optional<T> and ensures their usability in hash-based data structures. Container-based algorithms and associative storage structures such as std::unordered_set or std::unordered_map serve as primary interaction partners, requiring a deterministic hash value to distribute elements across internal storage buckets. The definition is declared in header ara/core/optional.h in global namespace std [SWS_CORE_01199], thereby forming a direct link between the core libraries of AUTOSAR and the standard containers of modern C++ development environments.

Lifecycle

As a pure function object specialization, std::hash<ara::core::Optional<T>> is characterized by a minimal lifecycle. Interpretation: The structure is likely designed as a trivial, stateless function object that neither allocates dynamic memory nor binds exclusive operating system resources. Question Q-ad1c004a72b9f1b2 (open) Instantiation typically occurs temporarily on the call stack or implicitly as a template parameter within enclosing containers. Since no internal state variables are maintained, destruction of the functor is also trivial and free of side effects. The sole functional entry point is call operator operator(), which is declared as a const member function [SWS_CORE_01199]. As a result, multiple concurrent threads can execute the same functor instance in parallel without additional synchronization mechanisms such as mutexes or locks, provided that the passed optional instances remain unmodified during the hash computation.

Usage Path

The regular usage path follows a straightforward flow without multi-stage initialization steps. The user or an associative container passes a const reference to an ara::core::Optional<T> object to function call operator operator() [SWS_CORE_01199]. The operator processes the argument and immediately returns the result as an integer value of type size_t [SWS_CORE_01199].

Sequence diagram: Typical flow of hash value computation for ara::core::Optional<T>. Sources: [SWS_CORE_01199]

Interpretation: During execution, the functor presumably first checks the engagement state of the passed optional object. Question (open) If the object contains a value, the functor is likely to compute the hash value of the encapsulated value of type T by delegating to the corresponding hashing logic. If, on the other hand, the optional is in an empty state, a constant, predefined hash value is presumably returned. The resulting value of type size_t subsequently allows the calling container to directly determine the target bucket or compare key structures.

Error Scenarios

Regarding error handling and robustness, the specialization provides maximum guarantees for safety-critical systems. Call operator operator() is explicitly provided with the specifier noexcept and declared as exception safe [SWS_CORE_01199]. Neither are error codes returned, nor can exceptions be emitted during computation. Interpretation: This non-throwing guarantee requires that the hash function of the underlying type T also satisfies the noexcept condition and causes no runtime errors. Question Q-d13957d23be4919e (open) If no valid specialization of std::hash exists for a type T, this already leads to a type error during compilation. Thus, no unexpected exceptional states occur at runtime, ensuring reliable use in fault-tolerant Adaptive AUTOSAR applications.