Make IEmbeddingGenerator contravariant on TInput

src/Libraries/Microsoft.Extensions.AI.Abstractions/Embeddings/IEmbeddingGenerator.cs

@@ -24,7 +24,7 @@ namespace Microsoft.Extensions.AI;
 /// are used which might employ such mutation.
 /// </para>
 /// </remarks>
-public interface IEmbeddingGenerator<TInput, TEmbedding> : IDisposable
+public interface IEmbeddingGenerator<in TInput, TEmbedding> : IDisposable
     where TEmbedding : Embedding
 {
     /// <summary>Generates embeddings for each of the supplied <paramref name="values"/>.</summary>

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Embeddings/GeneratedEmbeddingsTests.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading.Tasks;
 using Xunit;
 
 #pragma warning disable xUnit2013 // Do not use equality check to check for collection size.
@@ -243,4 +244,21 @@ public void Indexer_InvalidIndex_Throws()
         Assert.Throws<ArgumentOutOfRangeException>("index", () => embeddings[-1]);
         Assert.Throws<ArgumentOutOfRangeException>("index", () => embeddings[2]);
     }
+
+    [Fact]
+    public async Task Generator_SupportsCovariantInput()
+    {
+        var expectedGeneratedEmbeddings = new GeneratedEmbeddings<Embedding<float>>([new Embedding<float>(new float[] { 1, 2, 3 })]);
+
+        using IEmbeddingGenerator<object, Embedding<float>> acceptsObject = new TestEmbeddingGenerator<object, Embedding<float>>
+        {
+            GenerateAsyncCallback = (values, options, cancellationToken) => Task.FromResult(expectedGeneratedEmbeddings),
+        };
+
+        IEmbeddingGenerator<string, Embedding<float>> acceptsString = acceptsObject;
+
+        var actual = await acceptsString.GenerateAsync(["hello"]);
+
+        Assert.Same(expectedGeneratedEmbeddings, actual);
+    }
 }

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/TestEmbeddingGenerator.cs

@@ -6,23 +6,27 @@
 using System.Threading;
 using System.Threading.Tasks;
 
+#pragma warning disable SA1402 // File may only contain a single type
+#pragma warning disable CA1816 // Dispose methods should call SuppressFinalize
+
 namespace Microsoft.Extensions.AI;
 
-public sealed class TestEmbeddingGenerator : IEmbeddingGenerator<string, Embedding<float>>
+public class TestEmbeddingGenerator<TInput, TEmbedding> : IEmbeddingGenerator<TInput, TEmbedding>
+    where TEmbedding : Embedding
 {
     public TestEmbeddingGenerator()
     {
         GetServiceCallback = DefaultGetServiceCallback;
     }
 
-    public Func<IEnumerable<string>, EmbeddingGenerationOptions?, CancellationToken, Task<GeneratedEmbeddings<Embedding<float>>>>? GenerateAsyncCallback { get; set; }
+    public Func<IEnumerable<TInput>, EmbeddingGenerationOptions?, CancellationToken, Task<GeneratedEmbeddings<TEmbedding>>>? GenerateAsyncCallback { get; set; }
 
     public Func<Type, object?, object?> GetServiceCallback { get; set; }
 
     private object? DefaultGetServiceCallback(Type serviceType, object? serviceKey) =>
         serviceType is not null && serviceKey is null && serviceType.IsInstanceOfType(this) ? this : null;
 
-    public Task<GeneratedEmbeddings<Embedding<float>>> GenerateAsync(IEnumerable<string> values, EmbeddingGenerationOptions? options = null, CancellationToken cancellationToken = default)
+    public Task<GeneratedEmbeddings<TEmbedding>> GenerateAsync(IEnumerable<TInput> values, EmbeddingGenerationOptions? options = null, CancellationToken cancellationToken = default)
         => GenerateAsyncCallback!.Invoke(values, options, cancellationToken);
 
     public object? GetService(Type serviceType, object? serviceKey = null)
@@ -33,3 +37,5 @@ void IDisposable.Dispose()
         // No resources to dispose
     }
 }
+
+public sealed class TestEmbeddingGenerator : TestEmbeddingGenerator<string, Embedding<float>>;