Initially adding KerasTensor. #1142

Author: Oceania2018

src/TensorFlowNET.Core/GlobalUsing.cs

@@ -3,4 +3,6 @@
 global using System.Text;
 global using System.Collections;
 global using System.Data;
-global using System.Linq;
+global using System.Linq;
+global using Tensorflow.Keras.Engine;
+global using Tensorflow.Framework.Models;

src/TensorFlowNET.Core/Keras/Layers/ILayersApi.cs

@@ -1,5 +1,6 @@
 using System;
 using Tensorflow.Framework.Models;
+using Tensorflow.Keras.Engine;
 using Tensorflow.Keras.Layers.Rnn;
 using Tensorflow.NumPy;
 using static Google.Protobuf.Reflection.FieldDescriptorProto.Types;
@@ -135,7 +136,7 @@ public ILayer EinsumDense(string equation,
         public ILayer GlobalMaxPooling1D(string data_format = "channels_last");
         public ILayer GlobalMaxPooling2D(string data_format = "channels_last");
 
-        public Tensors Input(Shape shape = null,
+        public KerasTensor Input(Shape shape = null,
             int batch_size = -1,
             string name = null,
             TF_DataType dtype = TF_DataType.DtInvalid,

src/TensorFlowNET.Core/Tensors/KerasTensor.cs

@@ -0,0 +1,40 @@
+namespace Tensorflow.Keras.Engine;
+
+/// <summary>
+/// A representation of a Keras in/output during Functional API construction.
+/// </summary>
+public class KerasTensor
+{
+    private Tensor _tensor;
+    public void SetTensor(Tensors tensor) 
+        => _tensor = tensor;
+
+    private TensorSpec _type_spec;
+    private string _name;
+
+    public KerasTensor(TensorSpec type_spec, string name = null)
+    {
+        _type_spec = type_spec;
+        _name = name;
+    }
+
+    public static KerasTensor from_tensor(Tensor tensor)
+    {
+        var type_spec = tensor.ToTensorSpec();
+        var kt = new KerasTensor(type_spec, name: tensor.name);
+        kt.SetTensor(tensor);
+        return kt;
+    }
+
+    public static implicit operator Tensors(KerasTensor kt)
+        => kt._tensor;
+
+    public static implicit operator Tensor(KerasTensor kt)
+        => kt._tensor;
+
+    public static implicit operator KerasTensor(Tensor tensor)
+        => from_tensor(tensor);
+
+    public static implicit operator KerasTensor(Tensors tensors)
+        => from_tensor(tensors.First());
+}

src/TensorFlowNET.Keras/BackendImpl.cs

@@ -76,7 +76,7 @@ public void track_variable(IVariableV1 v)
             _GRAPH_VARIABLES[graph.graph_key] = v;
         }
 
-        public Tensor placeholder(Shape shape = null,
+        public KerasTensor placeholder(Shape shape = null,
             int ndim = -1,
             TF_DataType dtype = TF_DataType.DtInvalid,
             bool sparse = false,

src/TensorFlowNET.Keras/GlobalUsing.cs

@@ -4,4 +4,5 @@
 global using System.Linq;
 global using static Tensorflow.Binding;
 global using static Tensorflow.KerasApi;
-global using Tensorflow.NumPy;
+global using Tensorflow.NumPy;
+global using Tensorflow.Keras.Engine;

src/TensorFlowNET.Keras/Layers/LayersApi.cs

@@ -466,7 +466,7 @@ public ILayer Flatten(string data_format = null)
         /// In this case, values of 'None' in the 'shape' argument represent ragged dimensions. For more information about RaggedTensors, see this guide.
         /// </param>
         /// <returns>A tensor.</returns>
-        public Tensors Input(Shape shape = null,
+        public KerasTensor Input(Shape shape = null,
             int batch_size = -1,
             string name = null,
             TF_DataType dtype = TF_DataType.DtInvalid,