Home/ Questions/Q 885505
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-15T12:55:21+00:00

I’m using some F# types ( Matrix et al) from C# and so I

  • 0

I’m using some F# types (Matrix et al) from C# and so I need to reference the FSharp.Core assembly in my C# project. So far, so good.

However, there are apparently some types defined in mscorlib.dll (v4) which are “duplicated” in FSharp.Core (v2), like System.Tuple and System.IObservable. I can’t understand why this is in .Net 4. Matt Ellis specifically said they would be removed in his MSDN article:

One language suffering that [duplication] problem was F#, which previously had defined its own tuple type in FSharp.Core.dll but will now use the tuple added in Microsoft .NET Framework 4.

I’m ready to look past this particular unseemly duplication if I could just specify which one I want to use in my C# program, however. When I try to use the System.Tuple type, for example, I get the following C# compiler error:

Error 2 The type ‘System.Tuple’ exists in both ‘c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework.NETFramework\v4.0\Profile\Client\mscorlib.dll’ and ‘c:\Program Files (x86)\Reference Assemblies\Microsoft\FSharp\2.0\Runtime\v2.0\FSharp.Core.dll’

The way around this, apparently, is a switch on the C# compiler command line which aliases the type:

csc.exe MyType.cs /reference:System.Tuple`2=mscorlib.dll /reference:FSharp.Core.dll

However, I can’t find a way to get Visual Studio to send this parameter to the C# compiler.

Anyone have a solution to this?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    You need to reference the 4.0 version of the F# runtime. This version corresponds with the 4.0 version of mscorlib and does not have the conflicting types. They will be in this directory

    C:\Program Files (x86)\Reference Assemblies\Microsoft\FSharp\2.0\Runtime\v4.0

    • 0