Macro builder 

macro_rules! builder {
    ($(#[$attr:meta])* $vis:vis $name:ident$(<$($g:ident),*>)? { $($(#[$field_attr:meta])* $field_name:ident: $field_type:ty $(=> { $(#[$setter_attr:meta])* $($t:tt)* })?),* }) => { ... };
}