HolderIterator flattens a collection of collections into a single iterator. It is designed for scenarios where you have an iterable of iterables (for example, the rows of a matrix or the segments of an IterationHolder) and want to traverse all elements in sequence without manually writing nested loops.
HolderIterator({
required Iterable<Iterable<E>> holder,
})
holder – an iterable whose elements are themselves iterables. Each inner iterable is treated as a row or segment. The iterator yields all elements of the first segment, then proceeds to the second, and so on until all segments have been exhausted.| Field | Description |
|---|---|
_holder |
Stores the outer iterable containing the segments. It is typically a list of lists or a list of Iteration objects. |
_outerIndex |
Zero‑based index of the current segment being traversed. Starts at 0. |
_innerIndex |
Index within the current segment. Initialised to −1 so that the first call to moveNext() sets it to 0. |
current – returns the element at _holder.elementAt(_outerIndex).elementAt(_innerIndex). Calling current before moveNext() throws a StateError.moveNext() – advances the iterator to the next element. It increments _innerIndex; if _innerIndex reaches the end of the current segment, it resets to 0 and increments _outerIndex to move to the next segment. Returns true while there are elements left and false once all segments are exhausted.HolderIterator is not intended to be used directly by library consumers. It is used internally by classes such as Matrix (to iterate over its rows) and IterationHolder (to iterate over concatenated lists) to provide a flattened view. Because it reads from the underlying iterables without copying, it is efficient for large data sets. However, it does not support modifying the underlying collections – it simply reads their elements in order.