The proposed solution for this Issue ( to use the max-munch principle
for the sequence [ [ ) seems to lead to exactly the same problem that C
++0x just got rid of with >> in templates, i.e. the examples from
N3034:

int p[10];
void f() {
    int x = 42;
    int(p[[x]{return x;}()]); // Error: malformed attribute on a nested
                                      // declarator-id and not a
function-style cast of
                                      // an element of p.
    new int[[]{return x;}()];  // Error even though attributes are not
allowed
}                                // in this context.

would become legal (and useful) code with introduced spaces:

     int(p[ [x]{return x;}()]);
    new int[ []{return x;}()];

or am I mistaken?
If I am not won't that introduce the same "minor, but persisting,
annoying, and somewhat embarrassing problem" that n1757 solves for
right angle brackets?






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On Mar 4, 10:06 am, Fabio Fracassi <f.fraca...@gmx.net> wrote:
> The proposed solution for this Issue ( to use the max-munch principle
> for the sequence [ [ ) seems to lead to exactly the same problem that C
> ++0x just got rid of with >> in templates, i.e. the examples from
> N3034:
>
> int p[10];
> void f() {
>     int x = 42;
>     int(p[[x]{return x;}()]); // Error: malformed attribute on a nested
>                                       // declarator-id and not a
> function-style cast of
>                                       // an element of p.
>     new int[[]{return x;}()];  // Error even though attributes are not
> allowed
>
> }                                      // in this context.
>
> would become legal (and useful) code with introduced spaces:
>
>      int(p[ [x]{return x;}()]);
>     new int[ []{return x;}()];
>
> or am I mistaken?
> If I am not won't that introduce the same "minor, but persisting,
> annoying, and somewhat embarrassing problem" that n1757 solves for
> right angle brackets?

No; the proposal prohibits the use of two consecutive [ tokens other
than to introduce an attribute. This is not a tokenization issue like
">>" was. Any amount of interior whitespace will make no difference. In
order to make the code legal, the lambda would have to be wrapped in
parentheses:

     int (p[([x]{return x;}())];

Sean


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On 5 Mrz., 19:05, Sean Hunt <ride...@gmail.com> wrote:
> On Mar 4, 10:06 am, Fabio Fracassi <f.fraca...@gmx.net> wrote:
> > ... won't that introduce the same "minor, but persisting,
> > annoying, and somewhat embarrassing problem" that n1757 solves for
> > right angle brackets?
>
> No; the proposal prohibits the use of two consecutive [ tokens other
> than to introduce an attribute. This is not a tokenization issue like
> ">>" was. Any amount of interior whitespace will make no difference. In
> order to make the code legal, the lambda would have to be wrapped in
> parentheses:
>
>      int (p[([x]{return x;}())];
>
> Sean
>

Which is also quite surprising, isn't it? And a similar embarrassment
while teaching C++? Well I guess it can't be helped.

regards

Fabio


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On Mar 7, 8:39 pm, Fabio Fracassi <f.fraca...@gmx.net> wrote:
> Which is also quite surprising, isn't it? And a similar embarrassment
> while teaching C++? Well I guess it can't be helped.
>
> regards
>
> Fabio

Having implemented the lookahead in clang, I can tell you it's not a
big deal (just scan ahead to the next ], taking nesting into account,
and see if it's followed by another one); I'm not a big fan of this
proposal myself.

Sean



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On 8 Mrz., 16:40, Sean Hunt <ride...@gmail.com> wrote:
> On Mar 7, 8:39 pm, Fabio Fracassi <f.fraca...@gmx.net> wrote:
>
> > Which is also quite surprising, isn't it? And a similar embarrassment
> > while teaching C++? Well I guess it can't be helped.
>
> > regards
>
> > Fabio
>
> Having implemented the lookahead in clang, I can tell you it's not a
> big deal (just scan ahead to the next ], taking nesting into account,
> and see if it's followed by another one); I'm not a big fan of this
> proposal myself.
>
> Sean
>
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I wouldn't know, since I have only theoretical knowledge regarding
compilers/parsers. I hope that your experience does count though and
makes the committee reconsider this proposal, and allow the
unsurprising syntax (i.e.  int (p[[x]{return x;}()];  )

Regards

Fabio


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