[llvm-dev] [cfe-dev] RFC: Plan for removing components from namespace std::experimental

Ben Craig via llvm-dev llvm-dev at lists.llvm.org
Mon Apr 10 13:27:30 PDT 2017

Sounds reasonable to me.  I believe expectations are set appropriately with the experimental namespace, and the extra, experimental library that needs to be linked in.

From: cfe-dev [mailto:cfe-dev-bounces at lists.llvm.org] On Behalf Of Marshall Clow via cfe-dev
Sent: Monday, April 10, 2017 3:23 PM
To: cfe-dev at lists.llvm.org; llvm-dev at lists.llvm.org
Subject: [cfe-dev] RFC: Plan for removing components from namespace std::experimental

As part of the work on C++17, WG21 released a series of "Technical Specifications", (TS) which added proposed new features to the standard library. These were all defined in the namespace 'std::experimental' (and namespaces inside of that).

Then, much of these features were merged into the main standard, and became part of namespace 'std'.  Libc++ now has two implementations of several of these, and they are diverging (because changes were made to the ones in the main standard, but not to the ones in the TS.

In the long run, I would like to remove the TS versions of these features from libc++ - since there are "better" versions in the main standard now. However, since people are using these, I don't think yanking them w/o warning is the right thing to do.

So, I'm proposing a new policy, and a timetable:

One year.

One year after we ship a LLVM release that supports a new C++ standard, we will remove all the features that are in the 'experimental' namespace that are implemented in the new standard).

Applying this policy to C++17,  we get:

LLVM 5.0 will support C++17.

So, for LLVM 7.0, we will remove (at least) the following features from libc++
* std::experimental::filesystem
* std::experimental::optional
* std::experimental::any
* std::experimental::string_view
* the searchers (std::experimental::boyer_moore, etc)
* std::experimental::random_shuffle

and probably other things...


-- Marshall

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