Re: technology discussion → does the world need a "new" C ?

On 2024-07-07, James Kuyper <jameskuyper@alumni.caltech.edu> wrote:

On 7/7/24 16:10, BGB wrote:

On 7/7/2024 9:03 AM, James Kuyper wrote:

On 7/7/24 00:55, BGB wrote:

On 7/6/2024 5:38 PM, Keith Thompson wrote:

...

No, there is no implicitly defined pointer.

...

This implicit pointer need not exist at a location in memory...

>
Which is why C doesn't give you access to it's location in memory -
something you complained about earlier.

>
I don't think I was claiming that one should have direct access to its
location or value within the language, rather that their existence and
behaviors could be acknowledged in the language design (for a "not
quite C" language).

>
I think that the existence of an implicit pointer would be a bad thing
to acknowledge, given that the language doesn't require that it exist,
and typical implementations don't use them. From what I understand, the
fact that your implementation does have implicit pointers makes it a rarity.

Ritchie's B language had arrays which contained a pointer to their
first element. Via a hack, it was possible to relocate an array.

In C, such a thing is not simply not required; it is ruled out
by the detailed semantic description of arrays.

The entire representation of an array of size N elements of type
T is contained in the memory block that is sizeo(T)*N bytes wide.

If you copy that block, you have a fully functional copy of the array.
No extra pointer needs to be set up with the correct value.

Furthermore, to dynamically allocate an array, you need only
provide sizeof(T)*N bytes of storage, and not a bit more.

There is simply nowhere in the representation of an array where
a pointer could hide that is part of the representation.

Code that manipulates arrays can be translated into something that
calculates a pointer. So a pointer can exist at run time, in a transient
way, perhaps in a register. That register can even be spilled into
memory. However, that's just part of the state of an evolving
calculation, not part of the representation of the array.

--
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca