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Document number: N4041

Date: 2014-05-23

Concerns with changing existing types in Technical Specifications

by Jonathan Wakely

Excerpts:

In Issaquah there were proposals targeting a TS which enhanced existing types in the Standard Library, in particular N3857 which modifies std::future, N3916 which modifies std::function, std::promise and std::packaged_task, and N3920 which modifies std::shared_ptr. ...

Following straw polls the decision was taken to allow a TS to change existing types in namespace std, so that users who opt in to use the TS (via some implementation defined means) get the enhanced versions without needing to change any code. ...

The decision made following the straw polls means for an implementation to ship a TS they must change existing classes in their implementation, which has the potential to make silent ABI changes to users' programs. ...

These issues can make it complicated for implementers to provide TS support, so that users have to wait longer before they have access to an implementation, which then makes it less likely the committee will get useful and timely feedback on the TS contents.

...