[API Proposal]: Add ServiceCollection.MakeReadOnly()

[halter73]

Background and motivation

The new HostApplicationBuilder in Microsoft.Extensions.Hosting and the MAUI host both implement custom IServiceCollection that change to read-only after the host is built. This means that ICollection<ServiceDescriptor>.IsReadOnly becomes true and any attempts to mutate the collection result in an InvalidOperationException. This makes it clear to developers that any attempt to modify services at this point is futile.

It would be nice if these hosts could use the default ServiceCollection to take advantage of potential perf improvements like those described in #44728.

API Proposal

namespace Microsoft.Extensions.DependencyInjection
{
    public class ServiceCollection
    {
+      public void MakeReadOnly();
    }
}

API Usage

public ServiceCollection ServiceCollection { get; } = new();

IHost Build()
{
    // BuildServiceProvider() is an extension method on IServiceProvider so it cannot
    // make the ServiceCollection read-only itself. It could after this change if it attempted to cast,
    // but that would be a breaking change and is not what I'm proposing.
    IServiceProvidier serviceProvider = ServiceCollection.BuildServiceProvider();
    ServiceCollection.MakeReadOnly();
    return serviceProvider.GetRequiredService<IHost>();
}

Alternative Designs

namespace Microsoft.Extensions.DependencyInjection
{
    public class ServiceCollection
    {
-      public bool IsReadOnly { get; }
+      public bool IsReadOnly { get; set; }
    }
}

I considered adding a setter to IsReadOnly, but I don't think it should be possible to transition a ServiceCollection from a read-only to a mutable state.

Risks

It adds additional API to ServiceCollection that shouldn't be called by the majority of developers interacting with the type. It's only really useful to library authors who build the ServiceCollection.

Context: #65109 (comment)

@eerhardt

[ghost]

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Issue Details

---

Background and motivation

The new HostApplicationBuilder in Microsoft.Extensions.Hosting and the MAUI host both implement custom IServiceCollection that change to read-only after the host is built. This means that ICollection<ServiceDescriptor>.IsReadOnly becomes true and any attempts to mutate the collection result in an InvalidOperationException. This makes it clear to developers that any attempt to modify services at this point is futile.

It would be nice if these hosts could use the default ServiceCollection to take advantage of potential perf improvements like those described in #44728.

API Proposal

namespace Microsoft.Extensions.DependencyInjection
{
    public class ServiceCollection
    {
+      public void MakeReadOnly();
    }
}

API Usage

public ServiceCollection ServiceCollection { get; } = new();

IHost Build()
{
    // BuildServiceProvider() is an extension method on IServiceProvider so it cannot
    // make the ServiceCollection read-only itself. It could after this change if it attempted to cast,
    // but that would be a breaking change and is not what I'm proposing.
    IServiceProvidier serviceProvider = ServiceCollection.BuildServiceProvider();
    ServiceCollection.MakeReadOnly();
    return serviceProvider.GetRequiredService<IHost>();
}

Alternative Designs

namespace Microsoft.Extensions.DependencyInjection
{
    public class ServiceCollection
    {
-      public bool IsReadOnly { get; }
+      public bool IsReadOnly { get; set; }
    }
}

I considered adding a setter to IsReadOnly, but I don't think it should be possible to transition a ServiceCollection from a read-only to a mutable state.

Risks

It adds additional API to ServiceCollection that shouldn't be called by the majority of developers interacting with the type. It's only really useful to library authors who build the ServiceCollection.

Author:	halter73
Assignees:	-
Labels:	api-suggestion, untriaged, area-Extensions-DependencyInjection
Milestone:	-

[terrajobst]

• Looks good as proposed

namespace Microsoft.Extensions.DependencyInjection;

public partial class ServiceCollection
{
    public void MakeReadOnly();
}