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Compiler Warning (level 2) CS0280 

Error Message

'type' does not implement the 'pattern name' pattern. 'method name' has the wrong signature.

Two statements in C#, foreach and using, rely on predefined patterns, "collection" and "resource" respectively. This warning occurs when the compiler cannot match one of these statements to its pattern due to a method's incorrect signature. For example, the "collection" pattern requires that there be a method called MoveNext which takes no parameters and returns a boolean. Your code might contain a MoveNext method that has a parameter or perhaps returns an object.

The "resource" pattern and using provide another example. The "resource" pattern requires the Dispose method; if you define a property with the same name, you will get this warning.

To resolve this warning, ensure that the method signatures in your type match the signatures of the corresponding methods in the pattern, and ensure that you have no properties with the same name as a method required by the pattern.

Example

The following sample generates CS0280.

// CS0280.cs
using System;
using System.Collections;

public class ValidBase: IEnumerable
{
   IEnumerator IEnumerable.GetEnumerator()
   {
      yield return 0;
   }

   internal IEnumerator GetEnumerator()
   {
      yield return 0;
   }
}

class Derived : ValidBase
{
   // field, not method
   new public int GetEnumerator;
}

public class Test
{
   public static void Main()
   {
      foreach (int i in new Derived()) {}   // CS0280
   }
}

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