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POVB Compiler does not do implicit casts to Object?
 

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  1. POVB Compiler does not do implicit casts to Object?
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    <p>I've recently had a strange issue with one of my APIs reported. Essentially for some reason when used with VB code the VB compiler does not do implicit casts to Object when trying to invoke the ToString() method.</p> <p>The following is a minimal code example firstly in C# and secondly in VB:</p> <pre><code> Graph g = new Graph(); g.LoadFromEmbeddedResource("VDS.RDF.Configuration.configuration.ttl"); foreach (Triple t in g.Triples) { Console.WriteLine(t.Subject.ToString()); } </code></pre> <p>The above compiles and runs fine while the below does not:</p> <pre><code> Dim g As Graph = New Graph() g.LoadFromEmbeddedResource("VDS.RDF.Configuration.configuration.ttl") For Each t As Triple In g.Triples Console.WriteLine(t.Subject.ToString()) Next </code></pre> <p>The second VB example gives the following compiler exception:</p> <blockquote> <p>Overload resolution failed because no accessible 'ToString' accepts this number of arguments.</p> </blockquote> <p>This appears to be due to the fact that the type of the property <code>t.Subject</code> that I am trying to write to the console has explicitly defined <code>ToString()</code> methods which take parameters. The VB compiler appears to expect one of these to be used and does not seem to implicitly cast to Object and use the standard <code>Object.ToString()</code> method whereas the C# compiler does.</p> <p>Is there any way around this e.g. a VB compiler option or is it best just to ensure that the type of the property (which is an interface in this example) explicitly defines an unparameterized <code>ToString()</code> method to ensure compatability with VB?</p> <h2>Edit</h2> <p>Here are the additional details requested by Lucian</p> <ol> <li>Graph is an implementation of an interface but that is actually irrelevant since it is the <a href="http://www.dotnetrdf.org/api/index.asp?Topic=VDS.RDF.INode" rel="nofollow">INode</a> interface which is the type that <code>t.Subject</code> returns which is the issue.<br> <a href="http://www.dotnetrdf.org/api/index.asp?Topic=VDS.RDF.INode" rel="nofollow">INode</a> defines two overloads for <code>ToString()</code> both of which take parameters</li> <li>Yes it is a compile time error</li> <li>No I do not use hide-by-name, the API is all written in C# so I couldn't generate that kind of API if I wanted to</li> </ol> <p>Note that I've since added an explicit unparameterized <code>ToString()</code> overload to the interface which has fixed the issue for VB users.</p>
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    1. USRobV
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    1. CONo cast should be needed. `.ToString()` is defined as public method on object class which is the subclass of all .net classes. So it's a member of each class you create. Even if you have overridden the method you can not change the access modifier to say `internal` - "no accessible 'ToString'" points me at this thought.
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    2. COYeah I know how and where `ToString()` is defined which is why am I so puzzled by the VB compiler complaining in this way. I though the person reporting this issue had just done something dumb but I've reproduced it myself so it is an issue of some sort with the VB compiler.
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    3. CO@Zebi And fwiw all the `ToString()` overloads are defined by an interface in this case so they have to be public, plus all the concrete implementations of the interface in question override the default `ToString()` method appropriately in addition to implementing the additional overloads
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