N4807 Editor’s Report: C++ Extensions for Library Fundamentals, Version 3

• N4806 is the current working draft. It revises N4786.
• N4807 is this Editor’s Report.

Change history and motions

There has been one motion since the previous revision:

• Kona 2019, LWG Motion 1: Move to apply the changes in P0052R10 (Generic Scope Guard and RAII Wrapper for the Standard Library) to the Library Fundamentals 3 working paper.

This paper has been applied with substantial editorial changes, for the following reason: The paper was written, and reviewed by LWG, to target the C++ IS working draft. However, following a decision by LEWG, the motion was to apply it to the Library Fundamentals TS instead. Since the TS is based on C++17, any wording that uses a new style of specification from the IS WD had to be “reverted” to the style used by C++17.

Specific editorial changes:

• C++20-style Mandates/Expects/Contraints elements have been rephrased as Requires/Remarks, using standard phrasing such as “This function/constructor shall not participate in overload resolution unless”.
• Edits to change the wording of the IS WD, [requirements] (with the purpose of allowing the destructor of scope_success to throw) have been replaced with new wording in [mods] that describe the edit. Additionally, the added permission for the paragraph “Remarks:” has been changed to “Throws:”, since the destructor in question does not actually have a “Remarks:” element, but only a “Throws:”.
• The namespaces and header names have been changed to include “experimental”.
• The requirements Cpp17{Destructible,MoveConstructible,CopyConstructible,MoveAssignable,CopyAssignable} have been changed to {Destructible,MoveConstructible,CopyConstructible,MoveAssignable,CopyAssignable}.
• The placeholder class name has been changed from scope_guard to scope-guard, as per our usual convention for names that are not actual type names.
• Stable labels have been changed; specifically, to avoid ambiguity with [intro.scope], and to shorten the word “unique_resource”.
• To avoid hanging paragraphs, non-normative, introductory wording has been dropped (the proposed paragraph 1 of 7.5 and paragraph 1 of 7.5.1; paragraphs 2 and 3 (with modifications) of 7.5.1 have been moved to 7.5.2.
• The description “factory function” has been renamed to “unique_resource creation”, similar to existing facilities of this kind.
• Introductory words “The class template” have been prepended to 7.5.2p1 so as to not start a sentence with a piece of code.
• The three separate constructor specifications for scope_exit, scope_fail, and scope_success have been merged into a single specification for the placeholder scope-guard, since they are largely analogous. Distinctions are called out by saying, “For scope_exit and scope_fail…”.
• The phrase “Throws: Nothing unless the initialization of exit_function throws” has been replaced with “Throws: Any exception thrown during the initialization of exit_function”, which we already use elsewhere and which seems more precise.

Editorial changes

All stable labels denoting synopses have been renamed to end in just “.syn”, not “.synop” or “.synopsis”, to follow the style of the IS. Moreover, a leading “header.” has been dropped from the stable labels of synopses.

Commit history

From the draft sources on GitHub.