Design Overview

Slot Call Iterator

Slot Call Iterator

The slot call iterator is conceptually a stack of iterator adaptors that modify the behavior of the underlying iterator through the list of slots. The following table describes the type and behavior of each iterator adaptor required. Note that this is only a conceptual model: the implementation collapses all these layers into a single iterator adaptor because several popular compilers failed to compile the implementation of the conceptual model.

Iterator Adaptor	Purpose
Slot List Iterator	An iterator through the list of slots connected to a signal. The `value_type` of this iterator will be `std::pair<any, connection>`, where the `any` contains an instance of the slot function type.
Filter Iterator Adaptor	This filtering iterator adaptor filters out slots that have been disconnected, so we never see a disconnected slot in later stages.
Projection Iterator Adaptor	The projection iterator adaptor returns a reference to the first member of the pair that constitutes a connected slot (e.g., just the `boost::any` object that holds the slot function).
Transform Iterator Adaptor	This transform iterator adaptor performs an `any_cast` to extract a reference to the slot function with the appropriate slot function type.
Transform Iterator Adaptor	This transform iterator adaptor calls the function object returned by dereferencing the underlying iterator with the set of arguments given to the signal itself, and returns the result of that slot call.
Input Caching Iterator Adaptor	This iterator adaptor caches the result of dereferencing the underlying iterator. Therefore, dereferencing this iterator multiple times will only result in the underlying iterator being dereferenced once; thus, a slot can only be called once but its result can be used multiple times.
Slot Call Iterator	Iterates over calls to each slot.