Should we consider sealed the newly introduced attributes for keyed service

[WeihanLi]

We introduced ServiceKeyAttribute and FromKeyedServicesAttribute for keyed service, while they are not sealed, and there're no inherits from the repo search result, since they're new types introduced, should we consider making them sealed?

From the sealed proposal #49944, we may prefer sealed for these types

keyed service PR: #87183

code search result:
https://github.com/search?q=repo%3Adotnet%2Fruntime%20ServiceKeyAttribute&type=code
https://github.com/search?q=repo%3Adotnet%2Fruntime%20FromKeyedServicesAttribute&type=code

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Issue Details

---

We introduced ServiceKeyAttribute and FromKeyedServicesAttribute for keyed service, while they are not sealed, and there're no inherits from the repo search result, since they're new types introduced, should we consider making them sealed?

From the sealed proposal #49944, we may need to prefer sealed for these types

keyed service PR: #87183

code search result:
https://github.com/search?q=repo%3Adotnet%2Fruntime%20ServiceKeyAttribute&type=code
https://github.com/search?q=repo%3Adotnet%2Fruntime%20FromKeyedServicesAttribute&type=code

Author:	WeihanLi
Assignees:	-
Labels:	untriaged, area-Extensions-DependencyInjection, needs-area-label
Milestone:	-

[ericstj]

I checked the transcript from the API review and found @benjaminpetit mentioned this was intentional:
https://www.youtube.com/live/PwB593iwQlk?feature=share&t=3454

[WeihanLi]

@ericstj thank you very much

[benjaminpetit]

By allowing inheritance on FromKeyedServicesAttribute, we allow people to use complex object as the key.

Here is an example:

public class CustomKey
{
    public CustomKey(int n, string str)
    {
        N = n;
        Str = str;
    }

    public int N { get; }
    public string Str { get; }
}

public sealed class FromServicesWithCustomKey : FromKeyedServicesAttribute
{
    public FromServicesWithCustomKey(int n, string str)
        : base(new CustomKey(n, str))
    {
    }
}

public class CustomService
{
    private readonly CustomKey _key;

    public CustomService([ServiceKey] CustomKey key)
    {
        _key = key;
    }

    public int N => _key.N;
    public string Str => _key.Str;
}

[Fact]
public void InheritanceTest()
{
    var serviceCollection = new ServiceCollection();
    serviceCollection.AddKeyedTransient<CustomService>(KeyedService.AnyKey);

    var provider = CreateServiceProvider(serviceCollection);

    var service = provider.GetKeyedService<CustomService>(new CustomKey(12, "hello"));

    Assert.Equal(12, service.N);
    Assert.Equal("hello", service.Str);
}