Upcoming language features

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Upcoming language features enable new (but potentially source breaking) functionality that be enabled by default in an upcoming language mode.

Overview

Upcoming language features allow the incremental adoption of language features that would otherwise only be available in a new language mode, without having to fully migrate to that mode. They can be enabled on the command line with -enable-upcoming-feature <feature>.

Some upcoming features have an additional "migration" mode, where the compiler will emit warnings with fix-its to help migrate to that mode. This can be enabled with -enable-upcoming-feature <feature>:migrate.

Topics

• doc:existential-any
• doc:member-import-visibility
• doc:nonisolated-nonsending-by-default