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    <p>Actually, it does neither. The <code>==</code> operator by default will test for reference equality, regardless of the overridden behavior of your <code>Equals</code> method (if you've overridden it, which you certainly should have if you implemented <code>IEquatable&lt;T&gt;</code>).</p> <p>That is to say, if your variables are typed as <code>object</code> but you want to use your own custom equality comparison, use <code>Equals(x, y)</code> rather than <code>x == y</code>.</p> <p>Then, even if you've implemented <code>IEquatable&lt;T&gt;</code>, be sure to <strong>still override <code>object.Equals</code></strong>, like this:</p> <pre><code>class MyType : IEquatable&lt;MyType&gt; { public bool Equals(MyType other) { // Whatever you want. } public override bool Equals(object other) { // Presumably you check for null above. return Equals(other as MyType); } } </code></pre> <p>While you certainly <em>can</em> also overload the <code>==</code> and <code>!=</code> operators for your type, this won't accomplish anything if you have references to objects of this type that are simply <code>object</code> variables, like this:</p> <pre><code>object x = new MyType(); object y = new MyType(); Console.WriteLine(Equals(x, y)); Console.WriteLine(x == y); </code></pre> <p>The above won't work as you might expect (if you've overloaded <code>==</code> and expect that to be used) because the <code>==</code> overload has to be resolved at compile-time; since <code>x</code> and <code>y</code> are typed as arbitrary objects, the C# compiler will pick the <code>object</code> type's <code>==</code> operator, which, again, just tests for reference equality.</p> <hr> <p><strong>Update</strong>: Now, you <em>can</em> ensure your <code>==</code> operator is used if your variables are typed as the class wherein you defined it <em>or</em> a more derived type. For example, given the following types:</p> <pre><code>class A { public static bool operator ==(A x, A y) { return true; } public static bool operator !=(A x, A b) { return false; } } class B : A { } class AComparer&lt;T&gt; where T : A { public bool CompareEqual(T x, T y) { return x == y; } } </code></pre> <p>The <code>AComparer&lt;T&gt;.CompareEqual</code> method above will use your overloaded <code>==</code> operator for <em>any</em> type <code>T</code> deriving from <code>A</code>.</p> <p>The key thing to remember is that <code>==</code> is <em>static</em>, which means its overload resolution gets performed at compile-time, not at run-time using a vtable (unless you're using <code>dynamic</code>, but that's a whole other beast). So just be aware of that whenever you're using the <code>==</code> operator in code and you want the overload to resolve to that of your custom type.</p>
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    1. POWhen I compare an Object (type) does it uses the IEquatable of a specific class?
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    1. USDan Tao
    1. USDan Tao
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    1. POWhen I compare an Object (type) does it uses the IEquatable of a specific class?
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    1. COAnd if use derivation constraints in my method. This change anything ? I can't overload the operator for object like equals ?
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      1. USThiago Bernabé
    2. CO@Dao-Tao, just to notify
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      1. USThiago Bernabé
    3. CO@Thiago: Sorry, I somehow missed your earlier comment. I *think* I understand what you are asking; give me a few minutes to update my answer.
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