Macro out_project 

macro_rules! out_project {
    {
        let $struct:ty { $($field:ident : $fieldty:ty),*$(,)? } = $src:ident;
    } => { ... };
}

Project an Out<struct X { field: Type }> to struct X { field: Out<Type> }.

It is allowed to include only a subset of the struct’s fields. The struct must implement OutProject.