Api change: Replace Ptr[Byte] with Ptr[_] where applicable.

[WojciechMazur]

Typically consumers of opaque inputs (void* in C) are good candidates for using Ptr[_]. This allows for better DX allowing to skip redundant .asInstanceOf[Ptr[Byte]] conversion.
Allocators malloc, calloc are still returniong Ptr[Byte] becouse it's literally what they do - these function return pointer to first byte of allocated area.

[ekrich]

Is this a wildcard type essentially because in C void* is a pointer to anything. So would that be Ptr[?] in Scala 3?

[WojciechMazur]

Is this a wildcard type essentially because in C void* is a pointer to anything. So would that be Ptr[?] in Scala 3?

Exactly. For Scala 2 and Scala 3 (under old syntax) Ptr[_] would be equivalent of void* It seems to fit Scala typesystem much better becouse of two reasons:

• easy consumption of opaque types: e.g. memcpy, memset
• protection against read of opaque type - Ptr[Any], and Ptr[_] cannot be loaded/assigned - there is no Tag for them. On Scala 2 there seems to be a Tag for Ptr[Nothing which is strange actually

While the other two Ptr[Any], Ptr[Nothing] could be used to protect against read/write of opaque data, these two would not be enough to easily pass pointers around. However, I'm open to suggestion if this change should be merged or for alternative approach

[ekrich]

No, this makes perfect sense. I just wondered if you could use Ptr[?] for the Scala 3 continuations site and if I was understanding correctly. Thanks for the explanation.

[LeeTibbert]

LGTM. This is a good step.

I checked, at a high level, that mentions in the documentation happened.

Looked like a couple of good type change/corrections in the network code. netdb.scala and
NetworkInterface (I think) caught my eye, but there were several other places: changing a Ptr[Byte] to a,
say, Ptr[addrinfo].

To make it easier for end users, one could consider adding as a teaching comment, just above the CString line:

"// type CVoidPointer = // The idiom for C void * is Ptr[_]"

/** The C/C++ 'void *' type; by convention, not declaration.
   *  type CVoidPointer =  Ptr[_] 
   */

That is where I have and would go looking for a suitable void * replacement.
One does not want to clutter the code; that is what doc is for and people
should read it. However, sometimes a clue about a very common transition
idiom is worth the noise.

If that appeals I can make a short PR after this merges. If you and/or other
reviewers decline the suggestion, I understand.

[WojciechMazur]

I've added the CVoidPtr type and adapted code to use it

[LeeTibbert]

re: CVoidPtr

I like what you did with the place. Nice change, especially in posixlib.