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

Michael S <already5chosen@yahoo.com> writes:

On Fri, 16 Aug 2024 01:08:15 +0100
Ben Bacarisse <ben@bsb.me.uk> wrote:
>

Bart <bc@freeuk.com> writes:
 

On 15/08/2024 15:33, Ben Bacarisse wrote: 

Bart <bc@freeuk.com> writes:
 

On 15/08/2024 09:43, Tim Rentsch wrote: 

Bart <bc@freeuk.com> writes: 

 

                          C call-by-value
call-by-reference ===============         =================
    at call:
>
      (array argument)    F(A)                    H(A)
>
      (pointer argument)  F(p)                    (disallowed) 

>
My posts were about passing *arrays* and the fact that C's
pass-by-value was remarkably similar to pass-by-reference. 

Which is why, presumably, you didn't show the differences.  Your
post was all polemic not part of a collegiate discussion of the
similarities and differences.
 

However your entry for pointers is not correct: 

No, the entry is correct.  H(p) would be (is?) disallowed when H's
parameter is a reference to an array. 

>
Sorry, what language does the right-hand column pertain to? /Any/
language that has call-by-reference, or Tim's hypthetical language?
 

 
Tim said that case was "disallowed".  You call that an error on his
part.  What language did you have in mind that permits such a gross
warping of types?  I would describe /any/ language that allowed it as
having a design error.
 

Or any that could be used to prove him right?
>
In general there is no reason, in a language with true
call-by-reference, why any parameter type T (which has the form U*,
a pointer to anything), cannot be passed by reference. It doesn't
matter whether U is an array type or not. 

 
I can't unravel this.  Take, as a concrete example, C++.  You can't
pass a pointer to function that takes an array passed by reference.
You can, of course, pass a pointer by reference, but that is neither
here nor there.

>
IMHO, C++ is a particularly bad example.

It's a bad example of a programming language, but that is exactly why
it's a good example of something very like C but with a reference
mechanism.

Yes, C++ has call-by-reference misfeature. But arrays in C++ are
2nd class citizen, same as in C. They can't be assigned and can't be
passed to callee, neither by value nor by reference.

See my reply to David.  If it has call-by-reference at all (and I agree
that passing reference values is a better way to think about this) then
why do say that arrays can't be passed by reference?  I'd say either
that nothing can (it's all just passing reference values) or arrays
/can/ indeed be "passed by reference" just like, say, int objects.

Also, I suspect that if you ask Ken Thompson, he will tell you that C++
does not really have 'call by reference'. Instead, it has references as
1st class object, so, naturally, values of references can be used
during 'call by value'.

I used to teach C++, and the only way to avoid a class full of puzzled
students is to avoid taking about "by reference" and "by value": all
argument passing is like local variable initialisation.  In essence,
everything is still passed by value.

So I agree with the general idea, but I would not say that references
are first class values, and reference objects are certainly not first
class objects (for example, you can't pass one "by reference"!).

I have enough of respect to KT to consider that his POV is not a
nonsense.
>

--
Ben.