Arbitrary Return Types for Register Modification Closures

[AdinAck]

Discussed in #859.

Added

• write_and
• write_with_zero_and
• modify_and

These functions return a T. The writer cannot be returned outside of the closure because the lifetime is constrained to remain within the function body.

Motivation

My reasons for this change are to allow strong type-state validity:

let state = rb.reg().write_and(|w| State::set(w.field()));

Thanks @burrbull!

[burrbull]

These functions return a T

Return a generic T which corresponds to type returned by passed closure.

Just a note.

[burrbull]

Instead of suffix it can be prefix.

What about external_write? ext_write

[AdinAck]

Hey great minds think alike, I was just thinking the same thing.

I was thinking from_write (but that's a bit close to From) and with_write.

[burrbull]

from_write sounds good

[AdinAck]

Ok well I guess we can tentatively go with from_* then. Thanks!

[AdinAck]

On a side note, to reduce duplicate code, I think the original methods could invoke the new ones with the generic T filled in. Will look into it later.

[burrbull]

cc @Emilgardis any comments?

[Emilgardis]

Would it make sense to put this behind a setting? I think not, but somethibg to maybe consider

[AdinAck]

Would it make sense to put this behind a setting? I think not, but somethibg to maybe consider

We discussed putting it behind a feature gate in the last meeting, but general consensus was against that idea.