Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/mscorlib/system/iformattable.cs

@@ -0,0 +1,32 @@
+// ==++==
+// 
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+// 
+// ==--==
+namespace System {
+    
+    using System;
+    using System.Diagnostics.Contracts;
+
+    [System.Runtime.InteropServices.ComVisible(true)]
+#if CONTRACTS_FULL
+    [ContractClass(typeof(IFormattableContract))]
+#endif // CONTRACTS_FULL
+    public interface IFormattable
+    {
+        [Pure]
+        String ToString(String format, IFormatProvider formatProvider);
+    }
+
+#if CONTRACTS_FULL
+    [ContractClassFor(typeof(IFormattable))]
+    internal abstract class IFormattableContract : IFormattable
+    {
+       String IFormattable.ToString(String format, IFormatProvider formatProvider)
+       {
+           Contract.Ensures(Contract.Result<String>() != null);
+ 	       throw new NotImplementedException();
+       }
+    }
+#endif // CONTRACTS_FULL
+}