UncheckedCastInEquals.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>
<overview>
<p>Since <code>Equals</code> takes an <code>object</code>, it can be passed an argument that has an 
arbitrary dynamic type: in particular, there is no guarantee that it is legal to cast the argument 
to the type that declares the <code>Equals</code> method. Code that does such a cast without checking 
the dynamic type of the argument first is therefore unsafe, and can break if an argument of 
the wrong dynamic type is passed in.</p>

</overview>
<recommendation>
<p>To fix the problem, test the dynamic type of the argument before performing such a cast.</p>

</recommendation>
<example>
<p>This example demonstrates casting of <code>object</code> to <code>UncheckedCastInEquals</code>. 
This can cause problems because if the object is not an <code>UncheckedCastInEquals</code> the 
program crashes with an <code>InvalidCastException</code>.</p>
<sample src="UncheckedCastInEquals.cs" />

<p>A simple fix is to confirm the cast will succeed before performing it.</p>
<sample src="UncheckedCastInEqualsFix.cs" />
</example>
</qhelp>