Macro define_constructor 

macro_rules! define_constructor {
    ($inner:ident : $inner_var:tt => fn $name:ident(), layout: $perform_layout:expr) => { ... };
    ($inner:ident : $inner_var:tt => fn $name:ident($typ:ty), layout: $perform_layout:expr) => { ... };
    ($inner:ident : $inner_var:tt => fn $name:ident( $($params:ident : $types:ty),+ ), layout: $perform_layout:expr) => { ... };
}