RuntimeHandles should implement IEquatable

[MichalStrehovsky]

Background and motivation

RuntimeTypeHandle is often used as a key in a dictionary. See hits on github: https://grep.app/search?q=dictionary%3Cruntimetypehandle. The search results include high profile libraries such a CsWinRt.

The runtime handles already implement strongly typed Equals(XXXHandle other) methods, but without the interfaces, dictionaries are going to use the Equals(object other) implementations instead, needlessly boxing the argument, unless a custom comparer is provided (it isn't in the above search results...).

API Proposal

namespace System
{
    public struct RuntimeTypeHandle : IEquatable<RuntimeTypeHandle>
    {
        // bool Equals(RuntimeTypeHandle) already exists
    }

    public struct RuntimeMethodHandle : IEquatable<RuntimeMethodHandle>
    {
        // bool Equals(RuntimeMehtodHandle) already exists
    }

    public struct RuntimeFieldHandle : IEquatable<RuntimeFieldHandle>
    {
        // bool Equals(RuntimeFieldHandle) already exists
    }
}

API Usage

No boxing.

Alternative Designs

No response

Risks

No response

[ghost]

Tagging subscribers to this area: @dotnet/area-system-runtime
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and motivation

RuntimeTypeHandle is often used as a key in a dictionary. See hits on github: https://grep.app/search?q=dictionary%3Cruntimetypehandle. The search results include high profile libraries such a CsWinRt.

The runtime handles already implement strongly typed Equals(XXXHandle other) methods, but without the interfaces, dictionaries are going to use the Equals(object other) implementations instead, needlessly boxing the argument, unless a custom comparer is provided (it isn't in the above search results...).

API Proposal

namespace System
{
    public struct RuntimeTypeHandle : IEquatable<RuntimeTypeHandle>
    {
        // bool Equals(RuntimeTypeHandle) already exists
    }

    public struct RuntimeMethodHandle : IEquatable<RuntimeMethodHandle>
    {
        // bool Equals(RuntimeMehtodHandle) already exists
    }

    public struct RuntimeFieldHandle : IEquatable<RuntimeFieldHandle>
    {
        // bool Equals(RuntimeFieldHandle) already exists
    }
}

API Usage

No boxing.

Alternative Designs

No response

Risks

No response

Author:	MichalStrehovsky
Assignees:	-
Labels:	api-suggestion, area-System.Runtime, api-ready-for-review
Milestone:	-

[terrajobst]

Video

• Looks good as proposed
• We should do a pass and find all structs that provide a custom Equals method without implementing IEquatable<T>
• This should probably be an analyzer

namespace System
{
    public struct RuntimeTypeHandle : IEquatable<RuntimeTypeHandle>
    {
        // bool Equals(RuntimeTypeHandle) already exists
    }

    public struct RuntimeMethodHandle : IEquatable<RuntimeMethodHandle>
    {
        // bool Equals(RuntimeMethodHandle) already exists
    }

    public struct RuntimeFieldHandle : IEquatable<RuntimeFieldHandle>
    {
        // bool Equals(RuntimeFieldHandle) already exists
    }
}

[jkotas]

This should probably be an analyzer

https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1066 ?

[stephentoub]

This should probably be an analyzer

https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1066 ?

Yes, we need to fix or suppress all of our occurrences and then turn it on:
#56082 (comment)

[MichalStrehovsky]

Fixed in #63358. IEquatable on all the other structs that have Equals should be a different issue, if we want such issue. Looks like one of those issues that are so big that we'll never get to them.

[stephentoub]

IEquatable on all the other structs that have Equals should be a different issue, if we want such issue. Looks like one of those issues that are so big that we'll never get to them.

I opened #63687 with the list for API review and #63690 with an implementation.