namespace std

In module core, namespace std provides template specializations of std::hash, std::tuple_size, and std::tuple_element for data types of the AUTOSAR Adaptive Platform. This enables the direct use of types such as ara::core::String, ara::core::Optional, ara::core::Variant, ara::core::Vector, and ara::core::Array in standard containers and with C++ tuple language facilities. A constraint is that for nested types, the contained data types must also have valid specializations at compile time.

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Context

In module core of the AUTOSAR Adaptive Platform, namespace std serves the seamless integration of platform-specific basic types into the C++ Standard Library. Instead of introducing new types, the namespace provides targeted template specializations of standardized helper classes. The interaction partners comprise three essential components: the generic types of the C++ Standard Library (in particular unordered associative containers and tuple utilities), the template specializations within std, and the data types ara::core::Array, ara::core::Monostate, ara::core::Optional, ara::core::String, ara::core::StringView, ara::core::Variant, and ara::core::Vector defined in module core.

Context diagram: Interplay between standard containers, the specializations in std, and the ara::core types. Sources: Payload declarations of module core

The specializations of std::hash enable adaptive core data types to be used directly as keys in standard containers such as std::unordered_map or std::unordered_set. In parallel, specializations std::tuple_size and std::tuple_element for ara::core::Array extend support for standardized metaprogramming interfaces and language facilities.

Usage Path

A typical usage path begins with the use of an ara::core data type in generic C++ code. For example, an application declares a hash table with keys of type ara::core::String or ara::core::Optional<T>. During insertion, erasure, or lookup, the container implicitly accesses std::hash<ara::core::String> or std::hash<ara::core::Optional<T>>, respectively, to determine the key hash value.

The specializations cover different data structures:

• Strings and views: std::hash<ara::core::String> and std::hash<ara::core::StringView> compute hash values over the contained character sequence.
• Composite types: std::hash<ara::core::Optional<T>>, std::hash<ara::core::Variant<...>>, and std::hash<ara::core::Vector<T, Allocator>> enable hashing of complex type structures. Interpretation: The specializations for ara::core::Optional and ara::core::Variant are likely based on the semantic behavior of the standardized archetypes and produce deterministic values for empty or unoccupied states. Question Q-c432b06f0ba32c5e (open)
• Stateless types: std::hash<ara::core::Monostate> provides a hash function for empty states, as typically used in variants.
• Tuple protocol: For fixed data fields, std::tuple_size<ara::core::Array<T, N>> provides the element count at compile time, while std::tuple_element<I, ara::core::Array<T, N>> determines the data type of position I. Interpretation: The specializations of std::tuple_size and std::tuple_element are thus likely to enable the use of ara::core::Array with structured bindings. Question Q-3abb70390e67dbce (open)

Error Scenarios

Since the elements in namespace std are exclusively template specializations, error scenarios occur primarily at compile time. Typical problem constellations include:

• Missing hashing capability of base types: If std::hash is instantiated for a nested type such as ara::core::Optional<T> or ara::core::Vector<T, Allocator>, a valid specialization of std::hash must also exist for element type T. If missing, this leads to a compilation error.
• Invalid indexing in the tuple protocol: Access to std::tuple_element<I, ara::core::Array<T, N>> with an index I >= N violates the template precondition and aborts the compilation process.

Interpretation: Error scenarios are likely to be essentially limited to compile-time errors in the case of incomplete type specializations or static range violations, as the specification excerpt defines no runtime error codes or exception interfaces. Question Q-8cda269c72bd701c (open)