Macro static_fields_sig 

macro_rules! static_fields_sig {
    () => { ... };
    ($($key:tt : $sig:expr),+ $(,)?) => { ... };
    (@key $key:literal) => { ... };
    (@key $key:block) => { ... };
}

Example

use whalescript::FieldsSig;

const MY_SIGNATURE: FieldsSig = whalescript::static_fields_sig! {
    "a": whalescript::field_sig!(Number),
    "b": whalescript::field_sig!(Option<Boolean>),
};