TraversableQueue

Simple queue that provides the user with an interface to query, manipulate and dequeue its content.

• non thread safe queue using a ring buffer
• provides a member function template with a callable non-type template parameter to statically generate the traversal functionality
• performant but compromises on encapsulation/seperation of concerns
• relies on functionality from function_signature and param_pack contained in the TMP_lib repo
• to be used for adding order-matching capabilites to the CppOrderBook2 project

TraversableQueue class template

template<typename ContentType, size_t length>
requires std::is_default_constructible_v<ContentType> && std::is_nothrow_copy_assignable_v<ContentType> &&
std::is_nothrow_copy_constructible_v<ContentType> && (std::has_single_bit(length))
struct TraversableQueue

• ContentType: type that will be enqueued
• type constaints ensure that queue elements can be default constructed when the queue object is constructed, (nothrow) copy assigned when an element is enqueued and (nothrow) copy constructed when it's dequeued
• length: max number of element the queue can contain, determines the size of the ring buffer
• constrained to powers of two to prevent costly modulus operations when computing indices in ring buffer

interfaces

enqueue

bool enqueue(const ContentType&) noexcept

• enqueues a new element
• returns true if enqueueing was successful, false if the queue was already filled to capacity so the new element could not be enqueued

dequeue

std::optional<ContentType> dequeue() noexcept

• dequeues an element from the queue
• returns a std::optional containing the dequeued element if the queue wasn't empty and an empty std::optional if it was

the traverser object

• centerpiece of the traverse_content method templates
• has to be constexpr
• has to be callable with a first argument of type TraverseStateType, a second of type ContentType& and an optional third argument of the users choosing (more arguments can obviously be passed if the second argument is a sum type)
• TraverseStateType is provided by the user via the choice of traveser
• has to return std::tuple<TraverseStateType, bool, bool>
• when iterating over content, TraverseStateType is returned during every iteration and passed to traverser in the next, thus tranferring state across iterations
• traverser may change the queue's content via its second argument
• the first bool in the return type indicates whether an element is to be dequeued, the second bool stops the traversal if true is returned
• if the first bool is false once (i.e. entry in currenct iteration is not dequeued), returning true in a later iteration constitutes an error, it's up to the user providing traverser to ensure that doesn't happen

traverse_content

template<auto traverser>
requires (function_signature::arg_types_t<traverser>::size == 3)
std::tuple_element_t<0, function_signature::ret_type_t<traverser>>
traverse_content(function_signature::arg_types_t<traverser>::template index_t<0> initial_state, function_signature::arg_types_t<traverser>::template index_t<3> arg) noexcept

• method template that takes a traverser object as a non-type parameter
• the properties of traverser described above are checked statically
• the method takes TraverseStateType as its first argument, signifying the initial state of traversal
• the second argument is optional and can be chosen by user (method template overload omitting the second argument is provided and has an analogous signature)
• type checks use function_signature and param_pack from the TMP_lib repo