---
title: Renamesystem_context_replaceabilitynamespace
document: P4031R0
date: 2026-02-23
audience: LEWG
reply-to:
  - "Ruslan Arutyunyan <ruslan.arutyunyan@intel.com>"
paper-type: proposal
---

# Abstract

This paper proposes to rename `system_context_replaceability` namespace.

# 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]](https://wg21.link/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`.

| **SF** | **F** | **N** | **A** | **SA** |
| --- | --- | --- | --- | --- |
| 2 | 1 | 6 | 5 | 1 |

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]](https://wg21.link/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.

# 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.

# References

[P3804R1] Lucian Radu Teodorescu, Ruslan Arutyunyan. 2025-12-15.
Iterating on parallel_scheduler.

https://wg21.link/p3804r1