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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c++
Subject: Re: thread about the pros and cons of lambdas, but more about cons
Date: Sat, 28 Sep 2024 04:06:40 -0700
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Michael S <already5chosen@yahoo.com> writes:

> On Thu, 26 Sep 2024 10:38:02 -0700
> Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>
>> Michael S <already5chosen@yahoo.com> writes:
>>
>>> On Thu, 26 Sep 2024 10:01:11 -0700
>>> Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>>>
>>>> Ben Bacarisse <ben@bsb.me.uk> writes:
>>>>
>>>>> Ben Bacarisse <ben@bsb.me.uk> writes:
>>>>>
>>>>>> ... You can,
>>>>>> instead, do this (untested):
>>>>>
>>>>> I should have tested!  Of course you have to change the capture
>>>>> (at least for core) from '=' to '&':
>>>>>
>>>>>>   #include <functional>
>>>>>>
>>>>>>   int floodfill4(
>>>>>>     unsigned char *grey,
>>>>>>     int width, int height,
>>>>>>     int x, int y,
>>>>>>     unsigned char target, unsigned char dest)
>>>>>>   {
>>>>>>     if (width < 1 || height < 1)
>>>>>>       return 0;
>>>>>>     if (x < 0 || x >= width || y < 0 || y >= height)
>>>>>>       return 0;
>>>>>>
>>>>>>     size_t w = width, h = height;
>>>>>>     if (grey[y*w+x] != target)
>>>>>>       return 0;
>>>>>>
>>>>>>     std::function<void(size_t, size_t)> core;
>>>>>>     core = [&] (size_t x, size_t y) {
>>>>>
>>>>> Corrected-----^
>>>>
>>>> Why do you think [&] should be used instead of [=]?
>>>
>>> Compiler says that otherwise 'core' captures itself before it
>>> properly initialize.
>>> And indeed, it does not work (Segmentation fault).
>>
>> Ahh.  A chicken and egg problem.  I sidestepped that by initializing
>> 'core' as part of its declaration (as my other response to Ben
>> shows).
>>
>> No compiler warning, but I didn't try running it.
>
> It does not make any difference.  The same crash as before.

Yes, not surprising.

> BTW, I am surprised that your compiler issues no warning.

Probably just an old compiler.  I'm not up-to-date with what's
going on with C++ so there isn't much incentive to upgrade.
Trying again with clang I do get a warning.