Abstract

This paper proposes to rename system_context_replaceability namespace.

1 Motivation

There was one attempt to rename system_context_replaceability. Unfortunately, it didn’t go well because likely the proposed alternatives for the names were not received well. [P3804R1] proposed several options favoring replacement and replacement_functions. As people pointed out, those names are probably also not great because they don’t give any sense of what developers try to replace. For example std::execution::replacement::receiver_proxy doesn’t help to understand what we’re actually replacing. The motivation to recommend either replacement or replacement_functions came because system_context_replaceability felt too long for a namespace name. However, people don’t seem to care about the length of the name. The poll below taken in Kona meeting (2025) shows that:

POLL: Change namespace system_context_replacability to replacement as proposed in P3804R0 Iterating on parallel_scheduler.

What is also important to note is that the poll was only about changing the current status quo to replacement. We have not voted for other options in [P3804R1]. Nevertheless, in my opinion we have to rename system_context_replaceability to something else because what we should care about is the consistency of C++ standard (whenever possible). Adding system_context_replaceability namespace name to C++26 will cause a lot of confusion because system_context does not even exist in the current working draft. Thus, users would not understand what they are actually replacing. What we have in the current working draft is actually named parallel_scheduler and the replaceability feature was developed specifically for it. I understand the argument that suggested replacement option perhaps does not give us what we want but it doesn’t eliminate the fact that we should rename system_context_replaceability to avoid even bigger confusion because std::execution::system_context_replaceability::receiver_proxy with no system_context presence anywhere in the C++ working draft is no better.

Based on the above either of parallel_scheduler_replaceability or parallel_scheduler_replacement name should be good enough because people seem to not be bothered by the name length and also because parallel_scheduler is exactly the name we have for the scheduler itself in the current working draft. Leaving the status quo would be a disaster, in my opinion.

2 Proposal

Option 1: Change std::execution::system_context_replaceability namespace name to std::execution::parallel_scheduler_replaceability.

Option 2: Change std::execution::system_context_replaceability namespace name to std::execution::parallel_scheduler_replacement.

Modify the formal wording in accordance with the winning option (if any wins compared to the status quo).

I like the second option slightly better because replaceability word means the feature to me and replacement sounds more like a set of the actual API. But I can live with any of those.

3 References