P3056 R0 what ostream exception

[wg21bot]

P3056R0 what ostream exception (Jarrad J. Waterloo)

[inbal2l]

LEWG Mailing list review for collecting feedback on P3056R0 was started on 2024-02-13

[inbal2l]

ML review closed by Steve Downey on 2024-03-06 (outcomes).
The author published a paper aims to encapsulate the feedback under a different number: P3170R0

Summary

Info from the thread (to be considered during the discussion):

Concerns:

• Virtual functions will not be called correctly and won't solve the issue.
• Request for the proposal to be implemented in a standard library implementation.
• Concern that implementation details "leak" to the proposal (if standard library implementation doesn't internally use a std::string to store its .what() message, or if copies of std::string are made).
• Proposal coupling ostreams and exceptions together.
• [exception]/2 ( https://eel.is/c++draft/exception#2), suggests there's no conforming implementation that can take advantage of this.
• Blanket C++03 requirement: result in std::terminate when an exception object copy constructor throws:
  "— when the exception handling mechanism, after completing evaluation of the expression to be thrown but before the exception is caught (15.1), calls a user function that exits via an uncaught exception,134)"

Suggestions supported:

• Addition of rvalue overloads: string&& taking constructors to potentially has value, as it does no harm and can potentially do good.
• (came up in the thread) Possibly adding a string_view versions of the constructors.

Related references (thanks, Zhihao):

• P2490: Zero-overhead exception stacktraces
• P2370: Stacktrace from exception

Next Steps

The new paper (P3170R0) will be reviewed by LEWGI