refactor: Optimize string handling capabilities

src/Core/Utilities/CssBuilder.cs

@@ -1,8 +1,10 @@
-namespace Microsoft.Fast.Components.FluentUI.Utilities;
+using System.Text;
+
+namespace Microsoft.Fast.Components.FluentUI.Utilities;
 
 public struct CssBuilder
 {
-    private string? stringBuffer;
+    private StringBuilder stringBuffer;
 
     /// <summary>
     /// Creates a CssBuilder used to define conditional CSS classes used in a component.
@@ -17,12 +19,14 @@ public struct CssBuilder
     /// </summary>
     public static CssBuilder Empty() => new();
 
+    public CssBuilder() => stringBuffer = new();
+
     /// <summary>
     /// Creates a CssBuilder used to define conditional CSS classes used in a component.
     /// Call Build() to return the completed CSS Classes as a string. 
     /// </summary>
     /// <param name="value"></param>
-    public CssBuilder(string? value) => stringBuffer = value;
+    public CssBuilder(string? value) => stringBuffer = new(value);
 
     /// <summary>
     /// Adds a raw string to the builder that will be concatenated with the next class or value added to the builder.
@@ -31,7 +35,7 @@ public struct CssBuilder
     /// <returns>CssBuilder</returns>
     public CssBuilder AddValue(string? value)
     {
-        stringBuffer += value;
+        stringBuffer.Append(value);
         return this;
     }
 
@@ -115,7 +119,7 @@ public CssBuilder AddClassFromAttributes(IReadOnlyDictionary<string, object> add
     public string? Build()
     {
         // String buffer finalization code
-        return stringBuffer?.Trim();
+        return stringBuffer.ToString().Trim();
     }
 
     // ToString should only and always call Build to finalize the rendered string.

src/Core/Utilities/StyleBuilder.cs

@@ -1,8 +1,10 @@
-namespace Microsoft.Fast.Components.FluentUI.Utilities;
+using System.Text;
+
+namespace Microsoft.Fast.Components.FluentUI.Utilities;
 
 public struct StyleBuilder
 {
-    private string? stringBuffer;
+    private StringBuilder stringBuffer;
 
     /// <summary>
     /// Creates a StyleBuilder used to define conditional in-line style used in a component. Call Build() to return the completed style as a string.
@@ -22,12 +24,14 @@ public struct StyleBuilder
     /// </summary>
     public static StyleBuilder Empty() => new();
 
+    public StyleBuilder() => stringBuffer = new();
+
     /// <summary>
     /// Creates a StyleBuilder used to define conditional in-line style used in a component. Call Build() to return the completed style as a string.
     /// </summary>
     /// <param name="prop"></param>
     /// <param name="value"></param>
-    public StyleBuilder(string prop, string value) => stringBuffer = $"{prop}: {value};";
+    public StyleBuilder(string prop, string value) => stringBuffer = new($"{prop}:{value};");
 
     /// <summary>
     /// Adds a conditional in-line style to the builder with space separator and closing semicolon.
@@ -42,7 +46,7 @@ public struct StyleBuilder
     /// <returns>StyleBuilder</returns>
     private StyleBuilder AddRaw(string? style)
     {
-        stringBuffer += style;
+        stringBuffer.Append(style);
         return this;
     }
 
@@ -146,7 +150,7 @@ public StyleBuilder AddStyleFromAttributes(IReadOnlyDictionary<string, object> a
     public string? Build()
     {
         // String buffer finalization code
-        return stringBuffer?.Trim();
+        return stringBuffer.ToString().Trim();
     }
 
     // ToString should only and always call Build to finalize the rendered string.

src/Core/Utilities/ValueBuilder.cs

@@ -1,10 +1,12 @@
-namespace Microsoft.Fast.Components.FluentUI.Utilities;
+using System.Text;
+
+namespace Microsoft.Fast.Components.FluentUI.Utilities;
 
 public class ValueBuilder
 {
-    private string? stringBuffer;
+    private StringBuilder stringBuffer = new();
 
-    public bool HasValue => !string.IsNullOrWhiteSpace(stringBuffer);
+    public bool HasValue => stringBuffer.Length > 0;
     /// <summary>
     /// Adds a space separated conditional value to a property.
     /// </summary>
@@ -16,9 +18,9 @@ public class ValueBuilder
 
     private ValueBuilder AddRaw(string? style)
     {
-        stringBuffer += style;
+        stringBuffer.Append(style);
         return this;
     }
 
-    public override string? ToString() => stringBuffer?.Trim();
+    public override string? ToString() => stringBuffer.ToString().Trim();
 }