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POGetting around Qt's templating restrictions
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  1. POGetting around Qt's templating restrictions
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    copied!<p>I want to write a simple flexible ftp server in C++ that can be parametrized with a class to handle the user (check login and password, deliver files etc.) supplied on server initialization.</p> <p>So I came up with this neat (so I thought) idea:</p> <pre class="lang-c prettyprint-override"><code>class FtpDelegate { public: FtpDelegate() {} virtual ~FtpDelegate() {} virtual bool login(QString username, QString password) = 0; // ... }; class DummyDelegate : public FtpDelegate { public: virtual bool login(QString username, QString password) { return true; } }; template&lt;class Delegate&gt; class FtpServer : public QObject, Derived_from&lt;Delegate, FtpDelegate&gt; { Q_OBJECT public: explicit FtpServer(const QHostAddress &amp;address = QHostAddress::Any, quint16 port = 21, QObject *parent = 0); public slots: void newConnection(); private: QTcpServer *server; QHostAddress address; }; template &lt;class Delegate&gt; void FtpServer&lt;Delegate&gt;::newConnection() { FtpDelegate *delegate = new Delegate(); new FtpConnection (delegate, server-&gt;nextPendingConnection(), address, this); } class FtpConnection : public QObject { Q_OBJECT public: explicit FtpConnection(FtpDelegate *delegate, QTcpSocket *socket, const QHostAddress &amp;address, QObject *parent = 0); public slots: void newDataConnection(); private: QTcpSocket *socket; QTcpServer *dataServer; // needed to transfer data to user QTcpSocket *dataSocket; }; // server initialization FtpServer&lt;DummyDelegate&gt; ftpServer(); </code></pre> <p>and then (you probably saw that coming) bam!</p> <pre><code>Error: Template classes not supported by Q_OBJECT </code></pre> <p>it is likely that there are other errors or misconceptions too as I am only starting to learn the C++ template mechanism (and Qt as well).</p> <p>My question is: what is the best way to make it work without using ugly hacks like passing function pointers or needing to create a factory implementation for each concrete FtpDelegate's derived class. Maybe there's some clever design pattern I just can't see. Eventually I can rewrite the network mechanism to boost if it is the best option.</p>
 

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