0.1.4

Chaining error messages

When dealing with an Error object, often you may want to pass the error up the call stack. As it is passed up the call stack, the level of abstraction is increased which can give increasing context to the error message. To facilitate this best practice, the Error object allows string concatenation with itself.

Fallible<User> GetUserFromDB(UserId id)
{
    if (!databaseIsConnected) return new Error("Database is not connected");
    ...
}

Fallible<User> FindUserById(UserId id)
{
    var (user, error) = GetUserFromDB(id);
    if (error) return "Could not find user: " + error;
    
    return user;
}

var (user, error) = FindUserById(id);
if (error)
{
    Console.WriteLine(error); // "Could not find user: Database is not connected"
}

Messages can also be appended by putting the string on the right hand side of the + operator.

return error + ": Could not find user";

Error message formatting

To ensure that error messages are not accidentally overwritten, directly setting the Error.Message property is not possible. If appending or prepending from the error message is not suitable, you can use the Error.Format method to format the message more comprehensively. This method functions exactly like the string.Format method and uses that in its implementation.

return error.Format("Could not find user: {0}: Aborting...", error.Message);