macro_rules! anonymous {
    {
        $($field_name:ident : $field_expr:expr),+
    } => {
        {
            #[allow(non_camel_case_types)]
            #[derive(Debug)] // Can add more derives here if wanted
            struct r#struct<$($field_name),+> {
                $($field_name: $field_name),+
            }

            r#struct {
                $($field_name: $field_expr),+
            }
        }
    };
    {
        $($field_name:ident : $field_expr:expr),+,
    } => {
        anonymous! { $($field_name : $field_expr),+ }
    }
}
struct r#struct {
    z: u32
}
fn main() {

    let y = anonymous! { x: r#struct { z: 0u32 } };
}