macro_rules! expand_custom_option_box { ($(impl Custom for Option<Box<$fname:ident>> ($func:ident, $extract:ident, $default: expr))*) => { ... }; }
macro_rules! expand_custom_option_box { ($(impl Custom for Option<Box<$fname:ident>> ($func:ident, $extract:ident, $default: expr))*) => { ... }; }