Macro utils_results::errcast

macro_rules! errcast {
    ($result : expr) => { ... };
    ($result : expr, $kind : ty $(, $format_str : expr $(, $val : expr) *) ?) => { ... };
}

Any type of error can be converted into our Master Error. (non panic unwraping)

// example
// <Unwraped Ok> = errcast!(<Any Result>, <Master Err>, <Optional,..>);
let num_read = errcast!(file.read(&mut buf), err::ReadErr, "this is {} data.", "meta");

also can

let num_read = errcast!(file.read(&mut buf));