Imported Upstream version 5.10.0.69

Former-commit-id: fc39669a0b707dd3c063977486506b6793da2890

mcs/class/corlib/ReferenceSources/String.cs

@@ -41,12 +41,25 @@ namespace System
 {
 	partial class String
 	{
+		[MethodImplAttribute (MethodImplOptions.InternalCall)]
+		public extern String (ReadOnlySpan<char> value);
+
 		public int Length {
 			get {
 				return m_stringLength;
 			}
 		}
 
+		public unsafe static implicit operator ReadOnlySpan<char> (String value)
+		{
+			if (value == null)
+				return default;
+
+			fixed (void* start = &value.m_firstChar)
+				return new ReadOnlySpan<char> (start, value.Length);
+		}
+
+
 		internal static unsafe int CompareOrdinalUnchecked (String strA, int indexA, int lenA, String strB, int indexB, int lenB)
 		{
 			if (strA == null) {
@@ -743,5 +756,17 @@ namespace System
 			// GetString () is called even when length == 0
 			return enc.GetString (bytes);
 		}
+
+		unsafe String CreateString (ReadOnlySpan<char> value)
+		{
+			if (value.Length == 0)
+				return Empty;
+
+			String result = FastAllocateString (value.Length);
+			fixed (char *dest = result, ptr = &value.DangerousGetPinnableReference ())
+				wstrcpy (dest, ptr, value.Length);
+
+			return result;
+		}
 	}
 }