error CS0111: Type 'SomeType' already defines a member called 'Equals' with the same parameter types

[jlaanstra]

Describe the bug
CsWinRT generates duplicate Equals methods if the underlying type in the WInMD already has an Equals() method with itself as the type parameter

To Reproduce
Create a C++WinRT component with a type that has an Equals method with itself as the equator. For example:

    runtimeclass SomeType
    {
        SomeType();

        Boolean Equals(SomeType someType);
    };

Pass the WinMD to CsWinRT.

Expected behavior
No error.

Version Info
CsWinRT 1.2.6

[angelazhangmsft]

We should investigate the built-in support behavior in .NET Native/.NET Core to see what they do

[angelazhangmsft]

With existing built-in .NET support for WinRT, default behavior for ToString, Equals(Object), and GetHashCode methods is provided for C# WinRT components. According to these docs, Windows Runtime classes that are written in C# or Visual Basic can override the Equals(Object) method overload.

@Scottj1s - is it possible to define/override the Equals method from a C++/WinRT component that is projected into C#/.NET 5?

[angelazhangmsft]

Looking into the existing .NET Native support:

If we have a C++/WinRT component with the following definition:

runtimeclass Class
    {
        Class();
        Boolean Equals(Class c);
    }

Consuming this component from a .NET Native (UWP) C# application, I see two Equals methods (overloaded):

public bool Equals(Class c); // in my RuntimeComponent
public virtual bool Equals(Object obj); // in System.Runtime - this method also appears if I don't define Equals in my C++/WinRT component

[jlaanstra]

It sounds like CsWinRT should probably not auto-generate the implementation of IEquatable<SomeType>. Thoughts? /cc @Scottj1s who added this in #249

[angelazhangmsft]

CsWinRT should ensure the IEquatable pattern of 5 methods is enforced, picking up any methods that the runtime component implements.

[Corillian]

I just ran into this problem 😭.

[pontin-pdftron]

Same problem here.
We have an old component in C++/CX which overrides Equals and when migrating to C++/WinRT got the same issue.