This library provides a safe, zero-overhead interface for guarding access to shared data via access to another singleton token. It is an extension of GhostCell to allow more general singletons besides branded tokens, enabling data to be 'static

This library also provides two singleton implementations by itself:

• A scoped, branded token as GhostCell via with_token
• Simple create-once singleton structs via new_singleton

Why SCell over:

GhostCell (and LCell from the qcell crate)

• With a concrete singleton type, SCell's can be 'static and thus stored in 'static data-structures.
• SCell usages do not have to be strictly scoped.
• SCell is strictly more flexible and provides a with_token method to emulate GhostCell.
• Erased zero-size references can be used with SCell, allowing truly zero-cost abstraction.

Other Cells from the qcell crate

• Creating a SCell does not require any reference to the owning type.
• SCells provide from_mut and similar interfaces: they are structural like Cell and GhostCell.
• SCells have no runtime cost.

Why not?

• Unlike GhostCell, more general usages for SCell have not been formally proven correct.
• Type signatures involving SCell can be slightly more verbose than other options.

Examples

See the examples directory for some code samples

new_singleton(pub Lock);
pub fn main() {
    let mut lock1 = Lock::new().expect("Called main twice");
    let cell1 = SCell::new(0);
    let cell2 = &cell1;

    cell1.borrow_mut(&mut lock1) += 1;

    assert_eq!(1, *cell2.borrow(&lock1));
}