Function FLKeyPath_EvalOnce 

pub unsafe extern "C" fn FLKeyPath_EvalOnce(
    specifier: FLSlice,
    root: FLValue,
    outError: *mut FLError,
) -> FLValue

Evaluates a key-path from a specifier string, for a given Fleece root object. If you only need to evaluate the path once, this is a bit faster than creating an FLKeyPath object, evaluating, then freeing it.