IncorrectEqualsSignature.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>
<overview>
<p>The intent of defining an <code>Equals(object)</code> method on a class is generally to ensure
that instances of that class are compared using it, both in client code and in library code. The 
standard <code>Equals(object)</code> method has an <code>object</code> parameter, so
<code>Equals(T)</code> methods where <code>T</code> is not <code>object</code>, will often not be
used in favor of <code>Equals(object)</code>.</p>

</overview>
<recommendation>
<p>Define an <code>Equals(object)</code> method that returns false if the object parameter is not of 
the type containing the method.</p>

</recommendation>
<example>
<p>In this example, the <code>Equals</code> method only takes an instance of <code>Bad</code> as a 
parameter.</p>
<sample src="IncorrectEqualsSignatureBad.cs" />

<p>In the revised example, <code>Equals(object)</code> is overridden and defined in terms of the
<code>Equals(Good)</code> method.
</p>
<sample src="IncorrectEqualsSignatureGood.cs" />
</example>
<references>

  <li>MSDN: <a href="https://msdn.microsoft.com/en-us/library/bsc2ak47.aspx">Object.Equals Method (Object)</a>.</li>

</references>
</qhelp>