Add more good/bad examples for ILogger (#1309)

* more good/bad examples for ILogger

* more examples

* simply the example

* add link to the official doc

docs/logs/getting-started/LoggerExtensions.cs

@@ -0,0 +1,33 @@
+// <copyright file="LoggerExtensions.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using System;
+using System.Runtime.CompilerServices;
+using Microsoft.Extensions.Logging;
+
+internal static class LoggerExtensions
+{
+    // https://docs.microsoft.com/aspnet/core/fundamentals/logging/loggermessage
+    private static readonly Action<ILogger, object, Exception> LogExAction = LoggerMessage.Define<object>(
+        LogLevel.Information,
+        new EventId(1, nameof(LogEx)),
+        "LogEx({obj}).");
+
+    public static void LogEx(this ILogger logger, object obj)
+    {
+        LogExAction(logger, obj, null);
+    }
+}

docs/logs/getting-started/Program.cs

@@ -14,6 +14,7 @@
 // limitations under the License.
 // </copyright>
 
+using System.Collections.Generic;
 using Microsoft.Extensions.Logging;
 
 public class Program
@@ -26,7 +27,33 @@ public class Program
         });
         var logger = loggerFactory.CreateLogger<Program>();
 
+        // unstructured log
         logger.LogInformation("Hello, World!");
-        logger.LogInformation("Hello from {name} {price}.", "artichoke", 3.99);
+
+        // unstructured log with string interpolation
+        logger.LogInformation($"Hello from potato {0.99}.");
+
+        // structured log with template
+        logger.LogInformation("Hello from {name} {price}.", "tomato", 2.99);
+
+        // structured log with strong type
+        logger.LogEx(new Food { Name = "artichoke", Price = 3.99 });
+
+        // structured log with anonymous type
+        logger.LogEx(new { Name = "pumpkin", Price = 5.99 });
+
+        // structured log with general type
+        logger.LogEx(new Dictionary<string, object>
+        {
+            ["Name"] = "truffle",
+            ["Price"] = 299.99,
+        });
+    }
+
+    internal struct Food
+    {
+        public string Name { get; set; }
+
+        public double Price { get; set; }
     }
 }