Type of captured variable

[nrc]

Previous discussion, Zulip

E.g., if matching a String with a @ "foo", should a have type String, &str, or &String?

One 'nice to have' is for a (an unconstrained variable) and a @ ... to have the same type.

Note that &String can always be coerced to &str, so in most contexts is strictly more general. I think that if we follow the 'match ergonomics' binding mode rules, then that decides if the variable should be used by move or ref (i.e., if a should have type String or &String or &mut String). Note that if we're matching Ptr<String> then we can only bind by move if Ptr: DerefMove, since DerefMove does not yet exist, this is a type error unless Ptr is Box.