Compiler Error CS1640

 

Updated: July 20, 2015

For the latest documentation on Visual Studio 2017 RC, see Visual Studio 2017 RC Documentation.

foreach statement cannot operate on variables of type 'type' because it implements multiple instantiations of 'interface', try casting to a specific interface instantiation

The type inherits from two or more instances of IEnumerator<T>, which means there is not a unique enumeration of the type that foreach could use. Specify the type of IEnumerator<T> or use another looping construct.

The following sample generates CS1640:

// CS1640.cs  
  
using System;  
using System.Collections;  
using System.Collections.Generic;  
  
public class C : IEnumerable, IEnumerable<int>, IEnumerable<string>  
{  
    IEnumerator<int> IEnumerable<int>.GetEnumerator()  
    {  
        yield break;  
    }  
  
    IEnumerator<string> IEnumerable<string>.GetEnumerator()  
    {  
        yield break;  
    }  
  
    IEnumerator IEnumerable.GetEnumerator()  
    {  
        return (IEnumerator)((IEnumerable<string>)this).GetEnumerator();  
    }  
}  
  
public class Test  
{  
    public static int Main()  
    {  
        foreach (int i in new C()){}    // CS1640  
  
        // Try specifing the type of IEnumerable<T>  
        // foreach (int i in (IEnumerable<int>)new C()){}  
        return 1;  
    }  
}  

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