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Compiler Error CS0579

Duplicate 'attribute' attribute

It is not possible to specify the same attribute more than once unless the attribute specifies AllowMultiple=true in its AttributeUsage.

The following example generates CS0579.

// CS0579.cs
using System;
public class MyAttribute : Attribute
{
}

[AttributeUsage(AttributeTargets.All,AllowMultiple=true)]
public class MyAttribute2 : Attribute
{
}

public class z
{
    [MyAttribute, MyAttribute]     // CS0579
    public void zz()
    {
    }

    [MyAttribute2, MyAttribute2]   // OK
    public void zzz()
    {
    }

    public static void Main()
    {
    }
}
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