Macro ic_memory_key 

macro_rules! ic_memory_key {
    ($stable_key:literal, $label:path, $id:expr $(,)?) => { ... };
    (key = $stable_key:literal, ty = $label:path, id = $id:expr $(,)?) => { ... };
    (key = $stable_key:literal, label = $label:literal, id = $id:expr $(,)?) => { ... };
}

Declare and open a validated MemoryManager slot by stable key.

The macro registers declaration metadata during static initialization and returns the validated default-runtime memory handle at expression use time.