Macro get_field 

macro_rules! get_field {
    ($($name:ident: &$T:ty),* $(,)?) => { ... };
    ($($name:ident: $T:ty),* $(,)?) => { ... };
    (@getter $name:ident: &$T:ty) => { ... };
    (@getter $name:ident: $T:ty) => { ... };
    (@get_mut $name:ident: $T:ty) => { ... };
    (@get $name:ident: &$T:ty) => { ... };
    (@get $name:ident: $T:ty) => { ... };
}