Proposal: Allow a narrow subset of std::views to replace base:: equivalents

[Jan Wilken Dörrie]

Hi everyone,

I would like to propose moving a small, specific subset of std::views from Banned to Allowed.

Background Historically, std::views and range adaptors were banned due to concerns regarding compile-time overhead, optimization difficulties, and the subjective readability issues of chaining with operator|.

However, since we recently deployed a Clang plugin that actively bans the use of operator| for range adaptors, the pipe syntax won't compile anyway. By relying on direct function call syntax (e.g., std::views::reverse(range)), we naturally discourage deeply nested chaining, which mitigates the worst compile-time hits and readability concerns.

Motivation Currently, we are reimplementing quite a bit of the standard view machinery directly in base. Specifically, we maintain base::Zip, base::Reversed, and base::RangeAsRvalues. It would be significantly easier and reduce our maintenance burden to just use the std::views equivalents directly.

Proposal

1. Update c++-features.md to explicitly allow the following specific views:

• std::views::zip (to replace base::Zip)

• std::views::reverse (to replace base::Reversed)

• std::views::as_rvalue (to replace base::RangeAsRvalues)

2. Migrate existing usages of these base:: utilities to std::views:: and eventually deprecate the base:: versions.

If in the future folks find other utilities from <ranges> helpful, you are highly encouraged to propose them on the mailing list as separate proposals. For example, std::views::transform or std::views::enumerate also seem pretty useful.

Thoughts?

Best regards,

Jan

[Nico Weber]

Do you have numbers on compile time cost? I imagine some of the cost comes from including headers?

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