Crate overlay_map

A two-layered map structure where the foreground is mutable and the background is preserved.

OverlayMap lets you insert values without cloning, while keeping a single layer of historical context. Each key has a current value (foreground) and may have a previous value (background), which is automatically managed during updates.

use overlay_map::Overlay;

let mut door = Overlay::new_fg("Alice");
println!("Present: {:?}, {:?}", door.fg(), door.bg());

for name in ["Bob", "Carol", "Dave", "Eve"] {
    if let Some(evicted) = door.swap(name) {
        println!("{evicted} left");
    }
    println!("Present: {:?}, {:?}", door.bg(), door.fg());
}

while let Some(pulled) = door.pull() {
    println!("{pulled} left");
}

println!("Present: {:?}, {:?}", door.bg(), door.fg());

Structs

Overlay

A two-layer value container used by OverlayMap to manage current and historical values.

OverlayIntoIter

OverlayMap

A two-layered map where each key holds a current (foreground) and optional historical (background) value.