Will there be standardization of scope guard/scope exit idioms?

Question

Running a lambda on scope exit seems like such a basic thing, I would expect it to be standardized. Things like unique_ptr are better, when they apply, but I find there is an endless supply of "one-off" destructors are needed, especially when leveraging C-style libraries. Does anyone know if this is coming?

Ribbing

In which cases are you using lambdas on scope exit? – Questionless

Waiting for thread pool work items to complete before closing the thread pool is a good example (even when an exception is thrown you still have to wait or it will crash the workers). It's always possible to create a full C++ wrapper for each thing you do, but its so much extra code in the cases where you use it one time. – Ribbing

Write a proposal? I happen to like Stefanus Du Toit's implementation (though I have no idea why he called it Auto) – Detritus

@Barry: That is actually Arthur O'Dwyer's implementation - see goo.gl/0t8bXR – Boyett

@Boyett Oops. Reading comprehension fail on my part. Though comment remains about Auto :) – Detritus

Answer 1

n4189 is a proposal to add make_scope_exit wrappers, and other similar resource handlers, to the language. It is based off of the relatively famous scope_guard talk.

The most recent "current paper status" from LWG is in 2013, prior to the above date.

The contents of C++1z (hopefully C++17) are yet to be determined.

C++1z status for clang does not mention it. C++1z TS for clang does not mention it.

The paper itself contains an example implementation. I do not know what licensing terms it is under.

Mandimandible

It seems to have passed LEWG, but looks like it will need better wording before it can be adopted. N4189's wording is pretty bad. – Voidance

Answer 2

It would appear that the current version of the scope exit paper, P0052, will be going into the Library Fundamentals v3, for likely adoption in the Post-C++17 standard.

In short, not gonna happen for C++17. Sorry.

Selector

Final comment that there tells about a proposal to move it to IS. Can't say whether it's gonna happen. – Uncivil

@pepper_chico What is IS? – Overmodest

@Jens: The International Standard. It didn't make it, btw. – Selector