Monday, March 27, 2023

Digest for comp.lang.c++@googlegroups.com - 4 updates in 2 topics

Pawel Por <porparek@gmail.com>: Mar 27 01:11PM -0700

Hello,
 
Assume there is a struct with a single member object. When creating the object of a struct I want the member object sometimes be copied and sometimes moved. Is the following approach correct ? Assume I don't want to use generic programing.
 
#include <utility>
 
struct Item
{
Item() {}
Item(const Item&) {}
Item(Item&&) {}
 
Item& operator=(const Item&) { return *this; }
Item& operator=(Item &&) { return *this; }
};
 
struct Container
{
Item item;
 
Container(const Item& item) : item(item) {} // copying
Container(Item&& item) : item(std::move(item)) {} // moving
};
 
 
int main(int argc, char **argv)
{
Item a;
 
Container cont(a); // copying
Container cont2(std::move(a)); // moving
 
return 0;
}
Jason Vas Dias <jason.vas.dias@ptt.ie>: Mar 27 10:59AM -0700

Good day -
 
I'd really like to be able to define functions with names like :
∀() (\U{FOR_ALL}), or ⭮() , or ⭯() , or :
8704 2200 (1 1) ∀ 'FOR ALL'
8705 2201 (1 1) ∁ 'COMPLEMENT'
8707 2203 (1 1) ∃ 'THERE EXISTS'
8708 2204 (1 1) ∄ 'THERE DOES NOT EXIST'

Why can't I use these characters in identifiers ?
 
Would there be any support for submitting an RFC to the standards groups
to allow implementations to have some sort of local UTF-8 character
white-list policy ?
 
ie. I'd like to develop extensions for GCC and Clang that will allow them
to load a UTF-8 character White-List file , then these characters would be
allowed regardless of what the standards say about valid identifier characters.
 
Next step is getting a complete dump of what GCC and Clang consider to
be valid UTF-8 identifier characters, which is not as straightforward as it
should be.
 
I'd most appreciate any helpful advice / informative comments.
 
Thanks & Best Regards,
Jason
Richard Damon <Richard@Damon-Family.org>: Mar 27 03:02PM -0400

On 3/27/23 1:59 PM, Jason Vas Dias wrote:
 
> I'd most appreciate any helpful advice / informative comments.
 
> Thanks & Best Regards,
> Jason
 
My understanding is that C++ basically just took the set of characters
for identifiers from the recommendation of the Unicode Standard for
"Identifiers" (XID_Start, XID_Continue). All the characters you
mentioned are defined (I beleive) as operators.
 
My one thought is that the Standard Committee wants to reserve the
operators from being identifies in case at some point a method is
defined to add new operators.
 
My guess is that GCC and Clang just implement the set defined by the
standard, which means going to the UNICODE standard that is applicable
for that compiler and looking at its definition of those classes. I
wouldn't be surprised if the build process just has as an input, the
Unicode class definition file, and a program that parses it to build the
needed code for the various things that need that information.
 
Of course, there is nothing to prevent an implementation from accepting
additional characters (possibly with a warning or an option) beyond the
defined set.
scott@slp53.sl.home (Scott Lurndal): Mar 27 07:08PM


>My one thought is that the Standard Committee wants to reserve the
>operators from being identifies in case at some point a method is
>defined to add new operators.
 
Actually, there's something to be said for sticking to the
portable character set for identifiers, such that the current locale
and or character set settings don't matter when compiling the source.
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