System.Core.dll in 4.0 added by default?

Question

I was playing around with VS2010 beta2. I noticed that if I try to add System.Core.dll to a project which does not already have a reference to that, in VS2010, it complains saying I cannot add that assembly as it is already referenced by the project system. Any idea why they are doing that in VS2010/4.0? Is it because they have forwarded few types to mscorlib from System.Core?

Answer 1

Not an answer for "why they are doing that", but could be helpful.

This is how I see the chain of actions that lead to implicit referencing System.Core.dll:

• You make a project in Visual Studio 2010. It generates .csproj with ToolsVersion=4.0. Suppose it will use MSBuild from .NET 4.
• Your .csproj imports Microsoft.CSharp.targets from $(MSBuildBinPath). I guess it will be c:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\Microsoft.CSharp.targets
• Microsoft.CSharp.targets imports Microsoft.Common.targets
• In .NET 4, Microsoft.Common.targets imports Microsoft.NETFramework.props
• In Microsoft.NETFramework.props you can find AdditionalExplicitAssemblyReferences node, which has a semicolon-separated list of assemblies. I found there System.Core.dll and a variable for later replacement.

So, to disable implicit reference of System.Core.dll, you can remove it from the list in AdditionalExplicitAssemblyReferences node in c:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\Microsoft.NETFramework.props.

After this, if you use, for example, System.Linq and have no reference to System.Core.dll in your project, you will logically get compile error, just like in Visual Studio 2008.

Answer 2

System.Core has been part of the required framework since 3.5, because it includes things like ExtensionAttribute and the LINQ Standard Query Operators. Similarly, if you create a 3.5 project in VS2008, it will automatically add a reference to System.Core for you.