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copied!<p><em>AS. the answer was extended few times, as more and more info was uncovered turning the question from "what is CType function?" to "How to convert OleVariant to a required Interface type?". Thus the answer gradually covers all those topics.</em></p> <p>So, you met unknown function in Microsoft Visual Basic code. What is one to do, when he meets something yet unknown? Go Google.</p> <p>Google.com with text <code>CType MSDN</code> gives us this link in its top results: <a href="http://msdn.microsoft.com/en-us/library/vstudio/4x2877xb.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/library/vstudio/4x2877xb.aspx</a></p> <blockquote> <p>Returns the result of explicitly converting an expression to a specified data type, object, structure, class, or interface. If no conversion is defined from expression to typename (for example, from Integer to Date), Visual Basic displays a compile-time error message.</p> </blockquote> <p>So we have to reproduce typecast in Delphi, preferably compile-type type-cast, if possible.</p> <p>Google.com with text <code>typecast docwiki</code> gives us this link in its top results: </p> <ul> <li><a href="http://docwiki.embarcadero.com/RADStudio/XE4/en/Expressions_(Delphi)#Typecasts" rel="nofollow noreferrer">http://docwiki.embarcadero.com/RADStudio/XE4/en/Expressions_(Delphi)#Typecasts</a></li> </ul> <p>Which in turn gives us one more link referenced in the text:</p> <ul> <li><a href="http://docwiki.embarcadero.com/RADStudio/XE4/en/Interface_References#Interface_Typecasts" rel="nofollow noreferrer">http://docwiki.embarcadero.com/RADStudio/XE4/en/Interface_References#Interface_Typecasts</a></li> </ul> <p>So you have two syntaxes to try. One you tried and ruled out - the one with AS operator. Then try another, direct typecast syntax. </p> <pre><code>stylesheet := IHTMLStyleSheet( document.styleSheets.item(0) ); </code></pre> <p>Sometimes if above fails it also helps doing double typecast, <code>Variant -> IUnknown -> certain interface</code>, but in many cases that is but redundant version of the upper code.</p> <pre><code>stylesheet := IHTMLStyleSheet( IInterface( document.styleSheets.item(0) ) ); </code></pre> <p>Well, now that it was told that the source expression datatype is <code>OleVariant</code> we can read documentation with more precise aim, about <code>Variant</code> datatype conversions (<code>OleVariant</code> is little different from <code>Variant</code> in modern Delphi):</p> <ul> <li>AS operator is applicable to classes, objects and interfaces. It is not applicable to <code>Variant</code> expressions. This answers the original "why we cannot..." question.</li> <li>Documentation on <code>Variant</code> type suggests converting it using direct typecast syntax.</li> </ul> <p>.</p> <pre><code>stylesheet := IInterface( document.styleSheets.item(0) ) as IHTMLStyleSheet; </code></pre> <p>If wished, you can even use (over?)defensive programming using <a href="http://docwiki.embarcadero.com/Libraries/XE2/en/System.Variants.VarType" rel="nofollow noreferrer">http://docwiki.embarcadero.com/Libraries/XE2/en/System.Variants.VarType</a> to check that you got <code>varUnknown</code> or <code>varDispatch</code> before attempting at getting <code>IUnknown</code> out of the returned value.</p> <p>PS. The question seems as a duplicate now.</p> <ul> <li><a href="https://www.google.ru/search?q=delphi+cast+olevariant+to+interface" rel="nofollow noreferrer">https://www.google.ru/search?q=delphi+cast+olevariant+to+interface</a></li> <li><a href="https://stackoverflow.com/questions/4938601">Getting an IStream from an OleVariant</a></li> <li><a href="https://stackoverflow.com/questions/16111060">How to cast OleVariant to IDispatch derived?</a></li> </ul>

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