[Python-Dev] Type of range object members

["Martin v. Löwis"]

Alexander Belopolsky wrote:
> Since on most platforms ssize_t is the same as long, the choice  
> between the two is just a matter of self-documenting code.

No, it would be an actual change: on Win64,
sizeof(Py_ssize_t)>sizeof(long).

> Speaking  
> of which, I find it unfortunate that the name Py_ssize_t was selected  
> for the typedef.  I would prefer Py_index_t.  The first time I saw  
> Py_ssize_t, I did not notice the double 's' and thought it was an  
> unsigned type.

Hmm. That you fail to read it correctly can hardly be an argument
against it.

> On the second look, I've realized that it is signed  
> and started wondering why not ptrdiff_t.  I understand that ssize_t  
> is defined by POSIX as the return type of functions such as "read"  
> that can return either size or -1 for error.  I don't think POSIX  
> mandates sizeof(size_t) == sizeof(ssize_t), but I may be wrong.

In the rationale (XRAT) they say

"This is intended to be a signed analog of size_t."

They don't mandate it to have the same size, but it is the expectation
that implementations typically will.

> I would agree that ptrdiff_t, although standard C, is not a very  
> intuitive name, but ssize_t is even less clear. 

In the discussion, ptrdiff_t was never brought up as an alternative
(intptr_t was; see the PEP for why it is unsuitable). ssize_t seemed
most natural to me since size_t is the C "number of bytes" type,
and we need a signed version of it.

Regards,
Martin