Overhaul `RefPtr` and `String`

- `RefPtr` no longer tries to have distinct cases for interal-vs-external reference counts. Instead we always require an internal reference count.

  - Types the used `RefPtr` but weren't `RefObject` were made to inherit `RefObject`

  - The `ReferenceCounted` base class was removed, so that only `RefObject` remains

  - Implicit conversion from `RefPtr<T>` to `T*` added
    - This created some complicates for other types that relied on implicit conversions, so this isn't a net cleanup right now

- The main type that got messed up by the above was `String`, which previously held a `RefPtr<char, ...>`. This change thus *also* includes a major overhaul of `String`:

  - `String` now holds all its data via indirection, using a `StringRepresentation` that is a `RefObject`. This object holds a length, capacity, and directly stores the character data in its allocation. This means that `sizeof(String)==sizeof(void*)`

  - It is now possible to directly mutate a `String` by appending to its representation (we just need to ensure it has a reference count of `1`, possibly by cloning it). This means that `StringBuilder` is now basically just an idomatic use of `String`

  - A couple operations that just return sub-ranges of a `String` now return `StringSlice` to avoid allocation when it isn't needed. This required more work.

  - Indices into strings changed from `int` to `UInt` (which is pointer-sized). This had a bunch of follow-on changes because the value `-1` sometimes needs to be special-cased in code that uses indices. Further cleanups are probably needed here.

1 files changed, 33 insertions, 12 deletions

diff --git a/source/core/slang-io.cpp b/source/core/slang-io.cpp
index dc2793fc4..684fed0a1 100644
--- a/source/core/slang-io.cpp
+++ b/source/core/slang-io.cpp
@@ -40,24 +40,46 @@ namespace Slang
 		sb.Append(newExt);
 		return sb.ProduceString();
 	}
+
+    static UInt findLastSeparator(String const& path)
+    {
+		UInt slashPos = path.LastIndexOf('/');
+        UInt backslashPos = path.LastIndexOf('\\');
+
+        if (slashPos == -1) return backslashPos;
+        if (backslashPos == -1) return slashPos;
+
+        UInt pos = slashPos;
+        if (backslashPos > slashPos)
+            pos = backslashPos;
+
+        return pos;
+    }
+
 	String Path::GetFileName(const String & path)
 	{
-		int pos = path.LastIndexOf('/');
-		pos = Math::Max(path.LastIndexOf('\\'), pos) + 1;
-		return path.SubString(pos, path.Length()-pos);
+        UInt pos = findLastSeparator(path);
+        if (pos != -1)
+        {
+            pos = pos + 1;
+            return path.SubString(pos, path.Length() - pos);
+        }
+        else
+        {
+            return path;
+        }
 	}
 	String Path::GetFileNameWithoutEXT(const String & path)
 	{
-		int pos = path.LastIndexOf('/');
-		pos = Math::Max(path.LastIndexOf('\\'), pos) + 1;
-		int dotPos = path.LastIndexOf('.');
-		if (dotPos <= pos)
-			dotPos = path.Length();
-		return path.SubString(pos, dotPos - pos);
+        String fileName = GetFileName(path);
+		int dotPos = fileName.LastIndexOf('.');
+		if (dotPos == -1)
+            return fileName;
+		return fileName.SubString(0, dotPos);
 	}
 	String Path::GetFileExt(const String & path)
 	{
-		int dotPos = path.LastIndexOf('.');
+		UInt dotPos = path.LastIndexOf('.');
 		if (dotPos != -1)
 			return path.SubString(dotPos+1, path.Length()-dotPos-1);
 		else
@@ -65,8 +87,7 @@ namespace Slang
 	}
 	String Path::GetDirectoryName(const String & path)
 	{
-		int pos = path.LastIndexOf('/');
-		pos = Math::Max(path.LastIndexOf('\\'), pos);
+        UInt pos = findLastSeparator(path);
 		if (pos != -1)
 			return path.SubString(0, pos);
 		else