Struct Bank 

pub struct Bank<G>
where
    G: Group,
{ /* private fields */ }

Available on crate feature bank only.

A witness that group G’s bank is currently mapped.

This is the GhostCell-style permission token: a zero-sized value whose type G is the brand. Borrowing it shared (local) yields references into the bank; borrowing it &mut (a switch via scope) is what changes the mapping. Because you cannot do both at once, a reference obtained from local can never be live across a switch; the conflict is a borrow error.

The token is !Send and only mintable through assume (or, safely, the closure argument of scope).

Examples

fn play(b: &mut Bank<Sound>) {
    let note = *b.local(&MELODY);   // `b` proves Sound is mapped
    // ...
}

The token is !Send and !Sync: a “this bank is mapped” proof cannot cross threads, nor be parked in a static and read back later.

fn assert_send<T: Send>() {}
assert_send::<Bank<GroupZero>>(); // ERROR: Bank is !Send

fn assert_sync<T: Sync>() {}
assert_sync::<Bank<GroupZero>>(); // ERROR: Bank is !Sync

Implementations

impl<G> Bank<G>

where G: Group,

pub const unsafe fn assume() -> Bank<G>

Mint a token, asserting that group G’s bank is already mapped.

This is the escape hatch for hand-rolled control: after a raw switch_bank or inline asm, call assume to re-enter the safe local / scope API.

Safety

Group G’s bank must actually be mapped at the call site; otherwise every subsequent local/call through this token reads the wrong bank.

Trait Implementations

impl<G> !Send for Bank<G>

where G: Group,

impl<G> !Sync for Bank<G>

where G: Group,