CA1067: Override Equals when implementing IEquatable

Cause

A type implements IEquatable, but does not override Equals method.

Rule description

A type implementing IEquatable interface indicates that it supports comparing two instances of the type for equality. You should also override the base class implementations of Equals and GetHashCode() methods so that their behavior is consistent with that of the System.IEquatable.Equals implementation. For more information, see Notes to implementers.

Your Equals implementation should return results that are consistent with System.IEquatable.Equals implementation.

How to fix violations

To fix a violation, override Equals and implement it by invoking the System.IEquatable.Equals implementation. For example, the following two code snippets show a violation of the rule and how to fix it:

using System;

public struct S : IEquatable
{
    private readonly int _value;
    public S(int f)
    {
        _value = f;
    }

    public bool Equals(S other)
        => _value == other._value;
}

using System;

public struct S : IEquatable
{
    private readonly int _value;
    public S(int f)
    {
        _value = f;
    }

    public bool Equals(S other)
        => _value == other._value;

    public override bool Equals(object obj)
        => obj is S objS && Equals(objS);

    public override int GetHashCode()
        => _value.GetHashCode();
}