Macro impl_result 

macro_rules! impl_result {
    ($ok_struct_type:ident, $err_struct_type:ident, $struct_name:ident, copy = false, clone = false, [$($derive:meta),* ]) => { ... };
    ($ok_struct_type:ident, $err_struct_type:ident, $struct_name:ident, copy = false, [$($derive:meta),* ]) => { ... };
    ($ok_struct_type:ident, $err_struct_type:ident,  $struct_name:ident, [$($derive:meta),* ]) => { ... };
}