Re: Passing property Accesor as Function`

I think your real problem is making a generic handler is figuring out
the conversion functions. Once you have that, I don't see the difference
between what you have and:

pers.HourlyRate = PropertyParse<double?>(textRate.Text);

Besides maybe the additional type parameter.

My first stab is:

T PropertyParse<T>(string value) {
   return value.Length == 0 ? default(T) : (T) Convert.ChangeType(value,
typeof(T));
}

But ChangeType doesn't seem to work with nullables...Argh. So, how
about:

T PropertyParse<T>(string value) {
  Type realType = Nullable.GetUnderlyingType(typeof(T)) ?? typeof(T);
  return value.Length == 0 ? default(T) : (T) Convert.ChangeType(value,
realType);
}

Which passes the 2 minute SnippetCompiler test....Only downside is the
compiler isn't checking for a conversion operator because of ChangeType
- so you can get an InvalidCastException (of course, you already have to
deal with the FormatException with invalid input).

--MB

> -----Original Message-----
> From: Discussion of development on the .NET platform using any managed
> language [mailto:[email protected]] On Behalf Of Brady
> Kelly
> Sent: Monday, November 19, 2007 1:22 AM
> To: [email protected]
> Subject: [DOTNET-CLR] Passing property Accesor as Function`
> 
> Warning:  This is a purely academic and speculative post.
> 
> 
> 
> This has suddenly become a real 'would like to have' feature in the
> project
> I'm currently working on.  I know this isn't possible in standard C#,
> but
> I'm trying to find a hammer with the right weight and shape to beat
> this
> into some semblance of working.  What I would like to achieve is
> something
> like this, in the commented line:
> 
> 
> 
>     public class PersonForm
> 
>     {
> 
>         System.Windows.Forms.TextBox textRate = new TextBox();
> 
>         public void BuildPerson(Person person)
> 
>         {
> 
>             Person pers = new Person();
> 
>             pers.HourlyRate = textRate.Text.Length == 0 ? (double?)
> null :
> double.Parse(textRate.Text);
> 
>             // SetPropertyFromText(pers.HourlyRate, textRate.Text)
> 
>         }
> 
>     }
> 
> 
> 
> My SetPropertyFromText should take the pers.HourlyRate as a delegate
> parameter, not as a double?, determine the correct type conversion
> based on
> the type of the pers.HourlyRate, and set the property to the converted
> object value.
> 
> 
> 
> I can easily use a property name as my property parameter for
> SetPropertyFromText, but then I lose compile time checks.  Our
> generated
> DAL, nettiers, provides, for each entity, an Enum with all the column
> properties for each entity, and I think this is about as close as I've
> seen
> to what I want, but not quite there.
> 
> 
> 
> Any ideas on the matter?
> 
> 
> 
> 
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