Dynamic type conversion

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Hi guys, i need some help on this.
Im writing some code to match different parts of a string (html) using multiple regular expressions. Each expression return different types of data ex. decimal and uri.
Each expression is represented by a class PatternMatchDecimal, PatternMatchUri and inherit from the base class PatternMatchBase which will return a string and the inheriting classes will convert the match to the their respective types.

Ive defined a interface for the inhereting classes PatternMatchDecimal and PatternMatchUri.

C#

interface IPatternMatch
{
     bool Match(string html);
     T Parse<T>();
     object Result { get; }
     Type ResultType { get; }
}

Im using a factory to create the concrete types from the type of pattern.

C#

public class Pattern
{
     public string Regex { get; set; }
     public PatternType Type { get; set; }
}

IPatternMatch matchUri = PatternMatchFactory.CreatePatternMatch(Pattern);

The resulting data is to be collected in a response object.

C#

public class Response
{
       public Uri Uri { get; set; }
       public decimal Price { get; set; }
}

Now i need to convert the object Result from the IPatternMatch implementation of the regular expression to the type of the property in the Response object.

Something like this, which wont compile.

C#

Response.Uri = matchUri.Parse<Response.Uri.GetType()>();

Posted 6-May-11 0:36am

Homer77

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CodeHawkz 6-May-11 7:04am

Try,
Uri = matchUri.Parse<typeof(response.uri)>();

Homer77 6-May-11 13:43pm

That wont compile either :-(

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Sergey Alexandrovich Kryukov · Answer 1 · 2011-05-06T02:20:00

If your really implement Parse the way it can parse into any type (which is hard to believe, but let's assume if does it for some type(s)), I would expect it does this:

C#

IPatternMatch matchUri = //...
Response.Uri = matchUri.Parse<system.uri>(); 
</system.uri>

That is, the generic parameter should be known statically at the moment of compilation. I think this defeats the purpose of your design; and it means your whole design is wrong as you slightly misunderstood generics and mix it with OOP late binding (which one can assume looking at your last code line which would not compile).

This can be also seen from the fact that you Result property is of the base type Object and depends on the System.Type ResultType. If you used generic approach for this type, whole interface should be generic:

C#

interface IPatternMatch<T>
{
     bool Match(string html);
     T Parse();
     T Result { get; } //not really needed, I would assume
}

class IntegerMatch : IPatternMatch<int> 
{
     bool Match(string html) { return int.TryParse(html, out FResult); }
     int IPatternMatch<int>Parse(/* where is a string to parse? */) { /*...*/ }
     int IPatternMatch<int>Result { get { return FResult; /* when it's parsed */ } } 
     int FResult;
}

class UriMatch  : IPatternMatch<System.Uri> 
{ /*...*/ }

Is this idea enough for you to implement your desired behavior?
From my comments in the code you should see the interface should be changed.

That would work; and I don't see how your design could work. I cannot "fix" it though, because you did not explain your ultimate goal or general idea, because your explanation of "what you want" was "contaminated" with "how to do it". If you explained the "pure" idea or requirements, I would probably be able to offer a reasonable design.

—SA