added an extension method for saving statically typed model - adjust api changes & documentation example

Author: llRandom

docs/code/experimental/MlNetCookBookStaticApi.md

@@ -397,7 +397,7 @@ Here's what you do to save the model to a file, and reload it (potentially in a
 
 ```csharp
 // Saving and loading happens to 'dynamic' models, so the static typing is lost in the process.
-mlContext.Model.Save(model.AsDynamic, trainData.AsDynamic.Schema, modelPath);
+mlContext.Model.Save(model, trainData, modelPath);
 
 // Potentially, the lines below can be in a different process altogether.
 

src/Microsoft.ML.StaticPipe/ModelOperationsCatalog.cs

@@ -0,0 +1,42 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.IO;
+using Microsoft.ML.Data;
+
+namespace Microsoft.ML.StaticPipe
+{
+    public static class ModelOperationsCatalogExtensions
+    {
+        /// <summary>
+        /// Save statically typed model to the stream.
+        /// </summary>
+        /// <param name="catalog">The model explainability operations catalog.</param>
+        /// <param name="model">The trained model to be saved. Note that this can be <see langword="null"/>, as a shorthand
+        /// for an empty transformer chain. Upon loading with <see cref="ML.ModelOperationsCatalog.Load(Stream, out DataViewSchema)"/> the returned value will
+        /// be an empty <see cref="TransformerChain{TLastTransformer}"/>.</param>
+        /// <param name="dataView">The data view with the schema of the input to the transformer. This can be <see langword="null"/>.</param>
+        /// <param name="stream">A writeable, seekable stream to save to.</param>
+        public static void Save<TInShape, TOutShape, TTransformer>(this ML.ModelOperationsCatalog catalog, Transformer<TInShape, TOutShape, TTransformer> model, DataView<TInShape> dataView, Stream stream)
+            where TTransformer : class, ITransformer
+        {
+            catalog.Save(model?.AsDynamic, dataView?.AsDynamic.Schema, stream);
+        }
+
+        /// <summary>
+        /// Save statically typed model to the stream.
+        /// </summary>
+        /// <param name="catalog">The model explainability operations catalog.</param>
+        /// <param name="model">The trained model to be saved. Note that this can be <see langword="null"/>, as a shorthand
+        /// for an empty transformer chain. Upon loading with <see cref="ML.ModelOperationsCatalog.Load(Stream, out DataViewSchema)"/> the returned value will
+        /// be an empty <see cref="TransformerChain{TLastTransformer}"/>.</param>
+        /// <param name="dataView">The data view with the schema of the input to the transformer. This can be <see langword="null"/>.</param>
+        /// <param name="filePath">Path where model should be saved.</param>
+        public static void Save<TInShape, TOutShape, TTransformer>(this ML.ModelOperationsCatalog catalog, Transformer<TInShape, TOutShape, TTransformer> model, DataView<TInShape> dataView, string filePath)
+            where TTransformer : class, ITransformer
+        {
+            catalog.Save(model?.AsDynamic, dataView?.AsDynamic.Schema, filePath);
+        }
+    }
+}

src/Microsoft.ML.StaticPipe/ModelOperationsCatalogExtensions.cs

@@ -147,7 +147,7 @@ private void TrainRegression(string trainDataPath, string testDataPath, string m
             var metrics = mlContext.Regression.Evaluate(model.Transform(testData), label: r => r.Target, score: r => r.Prediction);
 
             // Saving and loading happens to 'dynamic' models, so the static typing is lost in the process.
-            mlContext.Model.Save(model.AsDynamic, trainData.AsDynamic.Schema, modelPath);
+            mlContext.Model.Save(model, trainData, modelPath);
 
             // Potentially, the lines below can be in a different process altogether.