err_des_1b.bal

import ballerina/io;

function foo() returns error? {
    return error("ErrReason", message = "err message", code = 123, bar = 45.6, baz = false);
}

public function main() {
    error? res = foo();

    if res is error {
        string errReason;
        string? errMessage;
        anydata|error errCode;
        anydata|error errPriority;

        // Since the unmatched fields could be of any type belonging to `anydata|error`, we use a 
        // `map<anydata|error>` to hold the rest of the fields.
        map<anydata|error> rest;

        // Only one rest binding pattern can be specified. 
        // Specified as `...var-name`.
        error(errReason, message = errMessage, code = errCode, priority = errPriority, ...rest) = res;

        io:println("errReason: ", errReason); // ErrReason
        io:println("errMessage: ", errMessage); // err message
        io:println("errCode is int: ", errCode is int); // true
        io:println("errPriority is (): ", errPriority is ()); // true
        io:println("length of rest: ", rest.length()); // 2 - bar and baz
    }
}