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On 16/08/2024 10:38, Michael S wrote:
> On Fri, 16 Aug 2024 02:18:15 -0700
> Keith Thompson <Keith.S.Thompson+u@gmail.com> wrote:
> 
>> Michael S <already5chosen@yahoo.com> writes:
>> [...]
>>> IMHO, C++ is a particularly bad example.
>>> 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.
>>>
>>> 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 have enough of respect to KT to consider that his POV is not a
>>> nonsense.
>>
>> Is that an attempt at proof by authority?
> 
> Yes!
> 
>> Not only does Ken Thompson
>> have very little to do with C++, but you're basing your conclusion on
>> what you *suspect* he would say.
>>
> 
> Yes, but it's not baseless.
> It is based on following section Go language FAQs that I assumed to be
> either authored or approved by KT.
> https://go.dev/doc/faq#pass_by_value


This seems to about what happens when a language has complex, two-level 
types where you have a descriptor, which has a pointer to the actual data.

The user may not be aware of that, and may think that passing such an 
object 'by-value' will copy the data. If the language only does 
'shallow' pass-by-value as seems to happen here, there may be some 
pass-by-reference semantics.

This can get confusing. However, whatever the machinations of a 
particular type, if a language offers *explicit* pass-by-reference, then 
you will always be able to provide real pass-by-reference on top.

So in the case of those descriptors, it will pass a reference to the 
descriptor. This allows a caller to modify what's in the descriptor, and 
have that change visible in the caller.

(My dynamic language has some 3-level types! There, reference parameters 
make a tangible difference.)