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POPassing Interface's method as parameter
 

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    <p>Is it possible to pass interface's method as parameters?</p> <p>I'm trying something like this:</p> <pre><code>interface type TMoveProc = procedure of object; // also tested with TMoveProc = procedure; // procedure of interface is not working ;) ISomeInterface = interface procedure Pred; procedure Next; end; TSomeObject = class(TObject) public procedure Move(MoveProc: TMoveProc); end; implementation procedure TSomeObject.Move(MoveProc: TMoveProc); begin while True do begin // Some common code that works for both procedures MoveProc; // More code... end; end; procedure Usage; var o: TSomeObject; i: ISomeInterface; begin o := TSomeObject.Create; i := GetSomeInterface; o.Move(i.Next); // somewhere else: o.Move(i.Prev); // tested with o.Move(@i.Next), @@... with no luck o.Free; end; </code></pre> <p>But it is not working because:</p> <blockquote> <p>E2010 Incompatible types: 'TMoveProc' and 'procedure, untyped pointer or untyped parameter'</p> </blockquote> <p>Of course I can do private method for each call, but that is ugly. Is there any better way?</p> <p>Delphi 2006</p> <hr> <p>Edit: I know that I can pass whole interface, but then I have to specify which function use. I don't want two exactly same procedures with one different call. </p> <p>I can use second parameter, but that is ugly too.</p> <pre><code>type SomeInterfaceMethod = (siPred, siNext) procedure Move(SomeInt: ISomeInterface; Direction: SomeInterfaceMethod) begin case Direction of: siPred: SomeInt.Pred; siNext: SomeInt.Next end; end; </code></pre> <hr> <p>Thanks all for help and ideas. Clean solution (for my Delphi 2006) is Diego's Visitor. Now I'm using simple ("ugly") wrapper (my own, same solution by TOndrej and Aikislave).</p> <p>But true answer is "there is no (direct) way to pass interface's methods as parameters without some kind of provider.</p>
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    1. COThe code in TSomeObject.Move looks like a use case for a 'Strategy' pattern. The MoveProc could be a method of a TAbstractMoveProcStrategy class, where subclasses implement the required behaviour in the Move method. TMovePredStrategy / TMoveNextStrategy would have different Move procs.
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