Imported Upstream version 4.3.2.467

Former-commit-id: 9c2cb47f45fa221e661ab616387c9cda183f283d

external/referencesource/mscorlib/system/FormattableString.cs

@@ -0,0 +1,82 @@
+// ==++==
+// 
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+// 
+// ==--==
+/*============================================================
+**
+** Class:  FormattableString
+**
+**
+** Purpose: implementation of the FormattableString
+** class.
+**
+===========================================================*/
+namespace System
+{
+    /// <summary>
+    /// A composite format string along with the arguments to be formatted. An instance of this
+    /// type may result from the use of the C# or VB language primitive "interpolated string".
+    /// </summary>
+    public abstract class FormattableString : IFormattable
+    {
+        /// <summary>
+        /// The composite format string.
+        /// </summary>
+        public abstract string Format { get; }
+
+        /// <summary>
+        /// Returns an object array that contains zero or more objects to format. Clients should not
+        /// mutate the contents of the array.
+        /// </summary>
+        public abstract object[] GetArguments();
+
+        /// <summary>
+        /// The number of arguments to be formatted.
+        /// </summary>
+        public abstract int ArgumentCount { get; }
+
+        /// <summary>
+        /// Returns one argument to be formatted from argument position <paramref name="index"/>.
+        /// </summary>
+        public abstract object GetArgument(int index);
+
+        /// <summary>
+        /// Format to a string using the given culture.
+        /// </summary>
+        public abstract string ToString(IFormatProvider formatProvider);
+
+        string IFormattable.ToString(string ignored, IFormatProvider formatProvider)
+        {
+            return ToString(formatProvider);
+        }
+
+        /// <summary>
+        /// Format the given object in the invariant culture. This static method may be
+        /// imported in C# by
+        /// <code>
+        /// using static System.FormattableString;
+        /// </code>.
+        /// Within the scope
+        /// of that import directive an interpolated string may be formatted in the
+        /// invariant culture by writing, for example,
+        /// <code>
+        /// Invariant($"{{ lat = {latitude}; lon = {longitude} }}")
+        /// </code>
+        /// </summary>
+        public static string Invariant(FormattableString formattable)
+        {
+            if (formattable == null)
+            {
+                throw new ArgumentNullException("formattable");
+            }
+
+            return formattable.ToString(Globalization.CultureInfo.InvariantCulture);
+        }
+
+        public override string ToString()
+        {
+            return ToString(Globalization.CultureInfo.CurrentCulture);
+        }
+    }
+}