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    <p>No, it's definitely <em>not</em> immutable. The <code>registered</code> value changes over the lifetime of the object.</p> <p>To make it immutable, you mustn't allow the <code>registered</code> field to change over the lifetime of the object - instead, make <code>Register</code> return a new object which has a <code>true</code> value for <code>registered</code></p> <p>I'd also remove the private setter for <code>SomeProperty</code>, just having a getter and a readonly variable.</p> <p>So something like this:</p> <pre><code>public class NewClass { private readonly bool registered; private readonly string someProperty; public bool Registered { get { return registered; } } public string SomeProperty { get { return someProperty; } } public NewClass Register() { // Note the change of exception here if (registered) { throw new InvalidOperationException("Already registered"); } return new NewClass(somePropertyFromDB, true); } // You may want to have a public constructor with just someProperty // which calls this one, which you could make private public NewClass(string someProperty, bool registered) { this.registered = registered.; this.someProperty = someproperty; } } </code></pre> <p>Some notes:</p> <ul> <li>Another option would be to have two separate classes, <code>RegisteredFoo</code> and <code>UnregisteredFoo</code>; that might make it easier to understand code using this class</li> <li>There's nothing to stop someone calling <code>Register</code> twice, so making this immutable doesn't really help in terms of idempotency. As there's a natural side-effect (talking to the database) it's hard to make this truly functional.</li> </ul>
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    1. COJon, thanks for your answer, but the setter for `SomeProperty` is marked as `private`. And as for the solution to the `registered` problem, even that way I can't assure that a user doesn't write `Instance1.Register(); Instance1.Register()`. Both of them will return a new object, but since I am keeping the original reference, I can execute the methods many times.
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    2. CO@User: Yes, I've only just noticed that and edited my answer. Editing further...
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