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RCS1241: Implement non-generic counterpart

Properties​

PropertyValue
Default SeverityHidden
Minimum language version-

Summary​

Publicly visible type that implements IComparable<T>, IComparer<T> or IEqualityComparer<T> should implement their non-generic counterpart.

Examples​

Example #1​

diagnostic.cs
using System;
using System.Collections.Generic;

public class C
{
}

public abstract class Comparable : IComparable<C>
{
    public abstract int CompareTo(C other);
}
fix.cs
using System;
using System.Collections.Generic;

public class C
{
}

public abstract class Comparable : IComparable<C>, IComparable
{
    public abstract int CompareTo(C other);

    public int CompareTo(object obj)
    {
        if (obj == null)
        {
            return 1;
        }

        if (obj is C x)
        {
            return CompareTo(x);
        }

        throw new ArgumentException("""", nameof(obj));
    }
}

Example #2​

diagnostic.cs
using System;
using System.Collections;
using System.Collections.Generic;

public class C
{
}

public abstract class Comparer : IComparer<C>
{
    public abstract int Compare(C x, C y);
}
fix.cs
using System;
using System.Collections;
using System.Collections.Generic;

public class C
{
}

public abstract class Comparer : IComparer<C>, IComparer
{
    public abstract int Compare(C x, C y);

    public int Compare(object x, object y)
    {
        if (x == y)
        {
            return 0;
        }

        if (x == null)
        {
            return -1;
        }

        if (y == null)
        {
            return 1;
        }

        if (x is global::C a
            && y is global::C b)
        {
            return Compare(a, b);
        }

        if (x is IComparable ic)
        {
            return ic.CompareTo(y);
        }

        throw new ArgumentException("""", nameof(x));
    }
}

Example #3​

diagnostic.cs
using System;
using System.Collections;
using System.Collections.Generic;

public class C
{
}

public abstract class EqualityComparer : IEqualityComparer<C>
{
    public abstract bool Equals(C x, C y);

    public abstract int GetHashCode(C obj);
}
fix.cs
using System;
using System.Collections;
using System.Collections.Generic;

public class C
{
}

public abstract class EqualityComparer : IEqualityComparer<C>, IEqualityComparer
{
    public abstract bool Equals(C x, C y);

    public abstract int GetHashCode(C obj);

    new public bool Equals(object x, object y)
    {
        if (x == y)
        {
            return true;
        }

        if (x == null || y == null)
        {
            return false;
        }

        if (x is global::C a
            && y is global::C b)
        {
            return Equals(a, b);
        }

        return x.Equals(y);
    }

    public int GetHashCode(object obj)
    {
        if (obj == null)
        {
            throw new ArgumentNullException(nameof(obj));
        }

        if (obj is C x)
        {
            return GetHashCode(x);
        }

        return obj.GetHashCode();
    }
}

Applies to​