Managed API: Refactoring and formatting.

Signed-off-by: Christoph M. Wintersteiger <cwinter@microsoft.com>

src/api/dotnet/StringSymbol.cs

@@ -0,0 +1,73 @@
+/*++
+Copyright (c) 2012 Microsoft Corporation
+
+Module Name:
+
+    StringSymbol.cs
+
+Abstract:
+
+    Z3 Managed API: String Symbols
+
+Author:
+
+    Christoph Wintersteiger (cwinter) 2012-11-23
+
+Notes:
+    
+--*/
+
+using System;
+using System.Runtime.InteropServices;
+using System.Diagnostics.Contracts;
+
+namespace Microsoft.Z3
+{
+
+    /// <summary>
+    /// Named symbols
+    /// </summary>
+    [ContractVerification(true)]
+    public class StringSymbol : Symbol
+    {
+        /// <summary>
+        /// The string value of the symbol.
+        /// </summary>
+        /// <remarks>Throws an exception if the symbol is not of string kind.</remarks>
+        public string String
+        {
+            get
+            {
+                Contract.Ensures(Contract.Result<string>() != null);
+
+                if (!IsStringSymbol())
+                    throw new Z3Exception("String requested from non-String symbol");
+                return Native.Z3_get_symbol_string(Context.nCtx, NativeObject);
+            }
+        }
+
+        #region Internal
+        internal StringSymbol(Context ctx, IntPtr obj)
+            : base(ctx, obj)
+        {
+            Contract.Requires(ctx != null);
+        }
+
+        internal StringSymbol(Context ctx, string s)
+            : base(ctx, Native.Z3_mk_string_symbol(ctx.nCtx, s))
+        {
+            Contract.Requires(ctx != null);
+        }
+
+#if DEBUG
+        internal override void CheckNativeObject(IntPtr obj)
+        {
+            if ((Z3_symbol_kind)Native.Z3_get_symbol_kind(Context.nCtx, obj) != Z3_symbol_kind.Z3_STRING_SYMBOL)
+                throw new Z3Exception("Symbol is not of string kind");
+
+            base.CheckNativeObject(obj);
+        }
+#endif
+        #endregion
+    }
+}