The "end game" of a Technical Specification (TS) is to have the features in there added to a future version of the C++ standard. When this happens, the TS can be retired. Sometimes, only part of at TS is added to the standard, and the rest of the features may be incorporated into the next version of the TS.
Adoption leaves library implementors with two implementations of a feature, one in namespace std, and the other in namespace std::experimental. The first one will continue to evolve (via issues and papers), while the other will not. Gradually they will diverge. It's not good for users to have two (subtly) different implementations of the same functionality in the same library.
As features are adopted into the main standard, we will implement them in namespace std, and then remove the versions in std::experimental. The removal will not happen immediately, because that would be unhelpful for users - giving them no chance to update their code.
The rule of thumb that libc++ will follow is: one year.
One year after we ship an implementation of a feature in std, we will remove it from std::experimental.
A specific example: The first release of clang/libc++ that officially supported C++17 was 5.0. For the 7.0 release (one year after 5.0), we will remove the features that were adopted into C++17 from the TSes, and that were present in namespace std in the 5.0 release.
Most (but not all) of the features of the LFTS were accepted into C++17.
|To be removed from|
|3.1.2||erased_type||Not part of C++17|
|3.3.1||All of the '_v' traits in <type_traits>||Removed|
|3.3.2||invocation_type and raw_invocation_type||Not part of C++17|
|3.3.3||Logical operator traits||Removed|
|3.3.3||Detection Idiom||Only partially in C++17|
|3.4.1||All of the '_v' traits in <ratio>||Removed|
|3.5.1||All of the '_v' traits in <chrono>||Removed|
|3.6.1||All of the '_v' traits in <system_error>||Removed|
|3.7||propagate_const||Not part of C++17|
|4.2||Enhancements to function|
|8.7||resource_adaptor||Not part of C++17|
|8.8||Access to program-wide memory_resource objects|
|8.9||Pool resource classes|
|8.11||Alias templates using polymorphic memory resources|
|8.12||Non-owning pointers||Not part of C++17|
|11.2||promise||Not part of C++17|
|11.3||packaged_task||Not part of C++17|
|12.4||shuffle||Not part of C++17|
|13.1||gcd and lcm||Removed|
|13.2||Random number generation||Not part of C++17|
|14||Reflection Library||Not part of C++17|
The FileSystem TS was accepted (in toto) for C++17.
The FileSystem TS implementation is still (as of v6.0) in namespace std::experimental.
Some (most) of the Parallelism TS was accepted for C++17.
We have not yet shipped an implementation of the Parallelism TS.
The Coroutines TS is not yet part of a shipping standard.
We are shipping (as of v5.0) an implementation of the Coroutines TS in namespace std::experimental.
The Networking TS is not yet part of a shipping standard.
We have not yet shipped an implementation of the Networking TS.
The Ranges TS is not yet part of a shipping standard.
We have not yet shipped an implementation of the Ranges TS.
The Concepts TS is not yet part of a shipping standard, but it has been adopted into the C++20 working draft.
We have not yet shipped an implementation of the Concepts TS.
None of the Concurrency TS was accepted for C++17.
We have not yet shipped an implementation of the Concurrency TS.
Last Updated: 8-Feb-2018