Rewriting a VB.NET Lambda expression as a C# statement

Question

I downgraded my app from version 4 of the framework to version 4 and now I want to implement this VB.NET lambda function statement (which works on 3.5)

Dim colLambda As ColumnItemValueAccessor = Function(rowItem As Object) General_ItemValueAccessor(rowItem, colName)

and rewrite it in C#. This was my attempt:

ColumnItemValueAccessor colLambda = (object rowItem) => General_ItemValueAccessor(rowItem, colName);

When I did this, I get the following error:

Error   14  One or more types required to compile a dynamic expression cannot be found. Are you missing references to Microsoft.CSharp.dll and System.Core.dll? C:\Source\DotNet\SqlSmoke\SqlSmoke\UserControls\ScriptUserControl.cs    84  73  SqlSmoke

However, when I downgraded the app from version 4.0 of the framework to 3.5 (because our users only hae 3.5 and don't have rights to install 4.0). when I did this, the reference to "Microsoft.CSharp" was broken.

Can I rewrite the VB.NET command in C# using syntax that is valid in C# 3.5 as I was able to in VB.NET? What would the syntax be?

I'm thinking that if I want to stay on 3.5, which is a must, then I have to write this code in VB.NET because it looks like C# got this functionality after VB.

namespace BinaryComponents.SuperList
{
    public delegate object ColumnItemValueAccessor(object rowItem);
}

private object General_ItemValueAccessor(DataRow rowItem, object colName)
{
    DataRow rowPerson = (DataRow)rowItem;
    return rowPerson[colName.ToString()].ToString();
}

Can you tell us how exactly ColumnItemValueAccessor and General_ItemValueAccessor are defined? — McGarnagle
– McGarnagle, Commented Aug 31, 2012 at 3:57

SLaks · Accepted Answer · 2012-08-31 03:37:44Z

1

Dynamic typing in C# is new to .Net 4.0.

Don't use dynamic.

answered Aug 31, 2012 at 3:37

SLaks

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3 Comments

Chad Over a year ago

Can you explain? I'm a bit new to this functionality. Perhaps, change the syntax of the line?

Dima Over a year ago

Perhaps you're using "dynamic" keyword somewhere in you program.

Chad Over a year ago

I used a code converter and didn't realize that "string colName = DataCol.ColumnName;" was previously defined as "dynamic colName = DataCol.ColumnName;." I thought the statements that I posted were using "dynamic typing." Until you mentioned that dynamic was a keyword, I searched for it and -- bingo. Thanks.

Nicolas Charette-Naud · Accepted Answer · 2012-08-31 03:42:24Z

0

Just be sure to have the right using

using System.Linq;

answered Aug 31, 2012 at 3:42

Nicolas Charette-Naud

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Comments

McGarnagle · Accepted Answer · 2012-08-31 04:18:02Z

0

The issue seems to be that one of the types don't match. Change the delegate parameter type from object to DataRow:

public delegate object ColumnItemValueAccessor(DataRow rowItem);

As AVD noted, you also need to fix the syntax on the lambda expression (the type object for rowItem is implied, it shouldn't be specified there):

ColumnItemValueAccessor colLambda = (rowItem) => General_ItemValueAccessor(rowItem, colName);

The key point is that when you write a lambda expression for the delegate type ColumnItemValueAccessor, the parameters and the return type of the lambda must match the delegate.

answered Aug 31, 2012 at 4:18

McGarnagle

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