Add internal String.{Try}CopyTo and use in a few places in corelib (#51062)

* Add internal String.{Try}CopyTo and use in a few places in corelib

We can use in more if it's made public.

* Apply suggestions from code review
Co-authored-by: NLevi Broderick <GrabYourPitchforks@users.noreply.github.com>
Co-authored-by: NLevi Broderick <GrabYourPitchforks@users.noreply.github.com>

src/libraries/Common/src/System/Text/ValueStringBuilder.cs

@@ -158,7 +158,12 @@ public void Insert(int index, string? s)
 
             int remaining = _pos - index;
             _chars.Slice(index, remaining).CopyTo(_chars.Slice(index + count));
-            s.AsSpan().CopyTo(_chars.Slice(index));
+#if SYSTEM_PRIVATE_CORELIB
+            s
+#else
+            s.AsSpan()
+#endif
+                .CopyTo(_chars.Slice(index));
             _pos += count;
         }
 
@@ -205,7 +210,12 @@ private void AppendSlow(string s)
                 Grow(s.Length);
             }
 
-            s.AsSpan().CopyTo(_chars.Slice(pos));
+#if SYSTEM_PRIVATE_CORELIB
+            s
+#else
+            s.AsSpan()
+#endif
+                .CopyTo(_chars.Slice(pos));
             _pos += s.Length;
         }
 

src/libraries/System.Private.CoreLib/src/System/Enum.cs

@@ -230,7 +230,7 @@ private static string ValueToHexString(object value)
 
             Span<char> resultSpan = new Span<char>(ref result.GetRawStringData(), result.Length);
             string name = names[foundItems[--foundItemsCount]];
-            name.AsSpan().CopyTo(resultSpan);
+            name.CopyTo(resultSpan);
             resultSpan = resultSpan.Slice(name.Length);
             while (--foundItemsCount >= 0)
             {
@@ -239,7 +239,7 @@ private static string ValueToHexString(object value)
                 resultSpan = resultSpan.Slice(2);
 
                 name = names[foundItems[foundItemsCount]];
-                name.AsSpan().CopyTo(resultSpan);
+                name.CopyTo(resultSpan);
                 resultSpan = resultSpan.Slice(name.Length);
             }
             Debug.Assert(resultSpan.IsEmpty);

src/libraries/System.Private.CoreLib/src/System/Exception.cs

@@ -176,7 +176,7 @@ public override string ToString()
 
             static void Write(string source, ref Span<char> dest)
             {
-                source.AsSpan().CopyTo(dest);
+                source.CopyTo(dest);
                 dest = dest.Slice(source.Length);
             }
         }

src/libraries/System.Private.CoreLib/src/System/Globalization/TimeSpanFormat.cs

@@ -269,7 +269,7 @@ private static bool TryFormatStandard(TimeSpan value, StandardFormat format, str
                 }
                 else
                 {
-                    decimalSeparator.AsSpan().CopyTo(destination);
+                    decimalSeparator.CopyTo(destination);
                     idx += decimalSeparator.Length;
                 }
                 WriteDigits(fraction, destination.Slice(idx, fractionDigits));

src/libraries/System.Private.CoreLib/src/System/Number.Formatting.cs

@@ -758,7 +758,7 @@ private static bool TryCopyTo(string source, Span<char> destination, out int cha
         {
             Debug.Assert(source != null);
 
-            if (source.AsSpan().TryCopyTo(destination))
+            if (source.TryCopyTo(destination))
             {
                 charsWritten = source.Length;
                 return true;

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.cs

@@ -960,7 +960,7 @@ public static unsafe IntPtr StringToHGlobalUni(string? s)
 
             IntPtr ptr = AllocHGlobal((IntPtr)nb);
 
-            s.AsSpan().CopyTo(new Span<char>((char*)ptr, s.Length));
+            s.CopyTo(new Span<char>((char*)ptr, s.Length));
             ((char*)ptr)[s.Length] = '\0';
 
             return ptr;
@@ -1007,7 +1007,7 @@ public static unsafe IntPtr StringToCoTaskMemUni(string? s)
 
             IntPtr ptr = AllocCoTaskMem(nb);
 
-            s.AsSpan().CopyTo(new Span<char>((char*)ptr, s.Length));
+            s.CopyTo(new Span<char>((char*)ptr, s.Length));
             ((char*)ptr)[s.Length] = '\0';
 
             return ptr;
@@ -1233,7 +1233,7 @@ public static unsafe IntPtr StringToBSTR(string? s)
 
             IntPtr bstr = AllocBSTR(s.Length);
 
-            s.AsSpan().CopyTo(new Span<char>((char*)bstr, s.Length)); // AllocBSTR already included the null terminator
+            s.CopyTo(new Span<char>((char*)bstr, s.Length)); // AllocBSTR already included the null terminator
 
             return bstr;
         }

src/libraries/System.Private.CoreLib/src/System/String.Manipulation.cs

@@ -1141,7 +1141,7 @@ private string ReplaceHelper(int oldValueLength, string newValue, ReadOnlySpan<i
                 thisIdx = replacementIdx + oldValueLength;
 
                 // Copy over newValue to replace the oldValue.
-                newValue.AsSpan().CopyTo(dstSpan.Slice(dstIdx));
+                newValue.CopyTo(dstSpan.Slice(dstIdx));
                 dstIdx += newValue.Length;
             }
 

src/libraries/System.Private.CoreLib/src/System/String.cs

@@ -447,6 +447,40 @@ public unsafe void CopyTo(int sourceIndex, char[] destination, int destinationIn
                 elementCount: (uint)count);
         }
 
+        // TODO: https://github.com/dotnet/runtime/issues/51061
+        // Make these {Try}CopyTo methods public and use throughout dotnet/runtime.
+
+        /// <summary>Copies the contents of this string into the destination span.</summary>
+        /// <param name="destination">The span into which to copy this string's contents.</param>
+        /// <exception cref="System.ArgumentException">The destination span is shorter than the source string.</exception>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal void CopyTo(Span<char> destination)
+        {
+            if ((uint)Length <= (uint)destination.Length)
+            {
+                Buffer.Memmove(ref destination._pointer.Value, ref _firstChar, (uint)Length);
+            }
+            else
+            {
+                ThrowHelper.ThrowArgumentException_DestinationTooShort();
+            }
+        }
+
+        /// <summary>Copies the contents of this string into the destination span.</summary>
+        /// <param name="destination">The span into which to copy this string's contents.</param>
+        /// <returns>true if the data was copied; false if the destination was too short to fit the contents of the string.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal bool TryCopyTo(Span<char> destination)
+        {
+            bool retVal = false;
+            if ((uint)Length <= (uint)destination.Length)
+            {
+                Buffer.Memmove(ref destination._pointer.Value, ref _firstChar, (uint)Length);
+                retVal = true;
+            }
+            return retVal;
+        }
+
         // Returns the entire string as an array of characters.
         public char[] ToCharArray()
         {