Referring to attributes in generic types?

I'm teaching myself C#, so forgive me if this seems slig开发者_高级运维htly obvious.

I'm trying to write a generic function that I can pass an array of structs into and then use one of the attributes of the struct. I have no idea how to declare a generic datatype in a function in a way that I can refer to attributes in the way needed.

Maybe what I'm asking can be better communicated in code - this is a non-working function to illustrate what I'm trying to do, how it strikes me as logical that it should work without actually knowing how to write it:

public static int AFunctionIsThis<DataType, int DataType.Value>(DataType passedrecord)
{
    temp = passedrecord.Value * 2 + 1;

    return temp;
}

And I want to be able to call it normally while specifying the attribute of the struct to be passed.

int NewVariable = AFunctionIsThis<ThisIsAStruct, ThisIsAStruct.AnIntAttribute>(ThisIsADeclaredStruct);

Thankyou very much,

Hanii Puppy.

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You can't specify members that a generic type should contain, you can only specify the generic data type.

You would use an interface where the property is defined:

public interface IHaveValue {
  int Value { get; }
}

Your struct would then implement the interface, and you can specify the interface as the generic data type:

public static int AFunctionIsThis<T>(T passedrecord) where T : IHaveValue {
  return passedrecord.Value * 2 + 1;
}

However, with what you are using it for, you don't need to use generics at all, you can just use the interface:

public static int AFunctionIsThis(IHaveValue passedrecord) {
  return passedrecord.Value * 2 + 1;
}

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Note that you should most likely not use a struct at all, but a class. A struct is more complicated to implement correctly, so you should stick to classes until you have a really good reason to use a struct.

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(To start with, note that the word "attribute" has a different meaning in .NET from the OOP sense.)

Use a Converter<T,int> and Action<T,int> delegate to get and set the member, respectively.

e.g.

public static int AFunctionIsThis<DataType>(DataType passedrecord, Converter<DataType,int> getter)
{
    temp = getter(passedrecord) * 2 + 1;

    return temp;
}

and then call it

AFunctionIsThis(ThisIsADeclaredStruct, x => x.AnIntProperty);

If you also need to set the value, you can use

AFunctionIsThis(ThisIsADeclaredStruct, x => x.AnIntProperty, (x, v) => { x.AnIntProperty = v; });

or do some magic with Expression<Converter<T>> to yank out the member reference and create a matching setter.

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Hanii Puppy:

In short, yes, you should be able to do what you are doing, but here is a syntax that works:

public static int AFunctionIsThis<T>(T passedRecord) where T : DataType
{
    var temp = passedRecord.Value;
    return temp;
}

public class DataType
{
    public int Value { get; set; }
}

Hope that helps. Dave

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What you want to do, is define a generic method that accepts only T that implements a certain interface or is derived from certain base class that has an int member called Value. e.g:

public interface IClass { int Value{get;set;} }
    public class ExampleImpl : IClass
    {
        int Value{get;set;}
        /* Additional Members\methods here */
    }
    public class HelperClass
    {
    public static int GenMethod<T>(T item) where T:IClass
    {
        return item.Value * 2 + 1;
    }
    }