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copied!<p><strong>Functionally</strong> there is no difference, they both return a value based on a parameter. In fact, properties are actually transformed into functions during compilation, since the notion of a <em>property</em> doesn't exist in <a href="http://en.wikipedia.org/wiki/Common_Intermediate_Language">MSIL</a>.</p> <p><strong>Semantically</strong>, however, there is a difference in how they <em>should</em> be used. Properties are meant as a way to expose the internal state of an object. Functions, on the other hand, are supposed to <em>operate</em> on an object's state to either provide an answer to a specific question (a <em>query</em>) or to modify the state in some way (a <em>command</em>).</p> <p>Here's an example:</p> <pre><code>Public Class Rectangle Private _size As Size ReadOnly Property Size() As Size Get Return _size End Get End Property Public Function IsSquare() As Boolean Return _size.Width = _size.Height End Function End Class </code></pre> <p>While <code>Size</code> simply exposes a <em>property</em> of the object, the <code>IsSquare</code> function actually <em>performs an operation</em> on the object's internal state in order to answer a question.</p> <p>Based on this principle, the most common use case for parameterized properties in VB.NET is in classes that <em>represent a sequence</em> of items, where the parameter is used to access a specific element in the sequence by its position or by some unique key. In other words, to create what's known as <a href="http://msdn.microsoft.com/en-us/library/6x16t2tx.aspx">indexers</a> in C#.</p>

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