TYPO3 Core

The Extension TER-list is using the SinglePagination, which lacks this method. But there is the list of items already present itself, so you can easily count in this case {extensions} (or any other array storing your data) to get the number needed.

I don't know this TER-list extension. But you mean SimplePagination, right? And with the list of items you mean the Paginator object that is separate from the Pagination object? Sure, one could use the Paginator objects getTotalAmountOfItems() method.

But then why separate the logic into Pagination and Paginator at all when I have to use both in order to render the "usual scenario" as depict in your screenshot? Imagine a partial used to render the Pagination would always have both objects present. Thus I vote for adding either getPaginator() or the beforementioned getTotalAmountOfItems() to the SimplePagination and/or the PaginationInterface.