Cast - string to Custom

Question

I have a custom wrapper object for my properties: MyType<t>. I have private members of these types and public members of type t.

I'm trying to load the object and am getting a cast error:

Unable to cast object of type 'System.String' to type 'Model.MyType`1[System.String]

I have a method for the following:

private t _value;

public static implicit  operator t(MyType<t> obj)
{
    return obj._value;
}

Any help in what I'm missing to make the cast work would be great.

Update:

The member looks like the following:

 MyType<string> PostalCode =  new MyType<string>();

I'm loading the properties with Dapper and the methods that were suggested are not being hit. So when the reflection engine tries to load the objects the implicit cast is not firing.

vcsjones · Accepted Answer · 2011-08-17T12:53:33.053

5

Your operator is backwards. It supports casting from MyType<t> to t. You want the other way around. Perhaps something like this is what you are looking for.

 private t _value;

 private MyType(t val)
 {
      _value = val;
 }

 public static implicit operator MyType<t>(t obj)
 {
     return new MyType<t>(obj);
 }

Using the constructor is optional, I personally just find that cleaner. You could just use the default constructor and set the field explicitly in your operator as well.

edited Aug 17 '11 at 12:53

answered Aug 17 '11 at 12:48

vcsjones

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That makes sense. However, the methods are not being hit. – Omnia9 Aug 17 '11 at 13:15
1

@Arnej65 Dapper might be trying to do an explicit cast then, which you can also override, change `implicit` to `explicit`. – Adam Houldsworth Aug 17 '11 at 13:21
I mixed it with this: http://stackoverflow.com/questions/5898988/map-string-to-guid-with-dapper – Omnia9 Aug 17 '11 at 15:19

Adam Houldsworth · Answer 2 · 2011-08-17T13:22:43.503

1

Your implicit cast operator is working in the reverse direction to what the error is complaining about, you need to implement the other implicit operator to go from t to MyType<t>.

You can also do the same with explicit casting (where you do something like string foo = (string)someObject;):

http://msdn.microsoft.com/en-us/library/xhbhezf4(v=vs.71).aspx

edited Aug 17 '11 at 13:22

answered Aug 17 '11 at 12:47

Adam Houldsworth

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Cast - string to Custom

Update:

2 Answers2