Enable chaining from StringBuilder.AppendSmart() and StringBuilder.Ap…

…pendLineSmart() (#452)

* Enable chaining from StringBuilder.AppendSmart() and StringBuilder.AppendLineSmart()
Fixes #451

* Add unit tests for chained StringBuilder.AppendSmart() and StringBuilder.AppendLineSmart()
#451

src/SmartFormat.Tests/Extensions/SmartExtensionsTests.cs

@@ -33,6 +33,17 @@ public void Test_AppendLine()
         Assert.That(actual, Is.EqualTo("these are the args" + Environment.NewLine));
     }
 
+    [Test]
+    public void Test_AppendLine_Chained()
+    {
+        var actual = new StringBuilder()
+            .AppendLineSmart("{0} {1} {2}", "these", "are", "the")
+            .Append("args")
+            .ToString();
+
+        Assert.That(actual, Is.EqualTo("these are the" + Environment.NewLine + "args"));
+    }
+
     [Test]
     public void Test_Append()
     {
@@ -44,6 +55,18 @@ public void Test_Append()
         Assert.That(actual, Is.EqualTo("these are the args"));
     }
 
+    [Test]
+    public void Test_Append_Chained()
+    {
+        var actual = new StringBuilder()
+            .AppendSmart("{0} {1}", "these", "are")
+            .Append(' ')
+            .AppendSmart("{0} {1}", "the", "args")
+            .ToString();
+
+        Assert.That(actual, Is.EqualTo("these are the args"));
+    }
+
     #endregion
 
     #region : TextWriterTests :

src/SmartFormat/SmartExtensions.cs

@@ -1,4 +1,4 @@
-// 
+//
 // Copyright SmartFormat Project maintainers and contributors.
 // Licensed under the MIT license.
 
@@ -19,20 +19,22 @@ public static class SmartExtensions
     /// <param name="sb">The StringBuilder that will be used for output</param>
     /// <param name="format">The template that defines how the arguments are formatted</param>
     /// <param name="args">A list of arguments to be used in formatting</param>
-    public static void AppendSmart(this StringBuilder sb, string format, params object[] args)
+    public static StringBuilder AppendSmart(this StringBuilder sb, string format, params object[] args)
     {
         var output = new StringOutput(sb);
         Smart.Default.FormatInto(output, format, args);
+        return sb;
     }
 
     /// <summary> AppendLines a formatted string, using the same semantics as Smart.Format. </summary>
     /// <param name="sb">The StringBuilder that will be used for output</param>
     /// <param name="format">The template that defines how the arguments are formatted</param>
     /// <param name="args">A list of arguments to be used in formatting</param>
-    public static void AppendLineSmart(this StringBuilder sb, string format, params object[] args)
+    public static StringBuilder AppendLineSmart(this StringBuilder sb, string format, params object[] args)
     {
         AppendSmart(sb, format, args);
         sb.AppendLine();
+        return sb;
     }
 
     #endregion
@@ -72,4 +74,4 @@ public static string FormatSmart(this string format, params object[] args)
     }
 
     #endregion
-}
+}