err_des_3.bal

import ballerina/io;

const MY_REASON = "MyReason";

type MyDetail record {|
    string message;
    error cause?;
    int code?;
    anydata|error...;
|};

type MyError error<MY_REASON, MyDetail>;

function foo() returns error? {
    return MyError(message = "err message", code = 123, bar = 12.3, baz = false);
}

public function main() {
    // Say I call a function returning either an `error` or `()`.
    error? res = foo();

    if res is MyError {

        string errMessage;
        int? errCode;
        map<anydata|error> rest;

        // Using an indirect error binding pattern.
        MyError(message = errMessage, code = errCode, ...rest) = res;

        io:println("errMessage: ", errMessage); // err message
        io:println("errCode is int: ", errCode is int); // true
        io:println("length of rest: ", rest.length()); // 2
    }
}