A puzzle and why generics are not generic enough right now

[bbatha]

@earthengine

&mut - My proposal

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At the “use” or “move” point, the old value get moved and finishes its lifetime. But a new “borrow” from the refered value being created on the same position, and have its own lifetime.

I think your new &mut proposal is a restatement of the Ref2Φ type discussed as a possibility for some of NLL work to accept nested &mut self method calls.

Accepting nested method calls with an `&mut self` receiver

Sure enough. And as we’re talking about 2-phase lifetimes, let me propose something that should “fix” this (with a change to Index): Add the possibility of “not-yet-active” lifetimes (ATM every lifetime has been active at some point). Find some hopefully-unhacky way of integrating this with lifetime inference. Add a Ref2Φ<'immut, 'mutbl, T> where T: 'immut, 'immut: 'mutbl reference type. Note that &'a T ~ Ref2Φ<'a, 'empty, T> &'a mut T ~ Ref2Φ<'a, 'a, T> Where the equivalence/coercion/what…