initializer list type deduction rules

From	Juha Nieminen <nospam@thanks.invalid>
Newsgroups	comp.lang.c++
Subject	initializer list type deduction rules
Date	2022-08-09 07:54 +0000
Organization	Aioe.org NNTP Server
Message-ID	<tct3rm$1l9a$1@gioia.aioe.org> (permalink)

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The exact type deduction rules for initializer lists are not completely
clear to me. For example, in an expression like this the type is deduced
without problems:

  std::pair<unsigned, unsigned> values[] =
      { { 1, 2 }, { 2, 3 }, { 3, 4 } };

However, here it's not:

  for(const std::pair<unsigned, unsigned>& value:
          { { 1, 2 }, { 2, 3 }, { 3, 4 } })

Sometimes it's useful to loop through a list of values using a range-based
for loop one-liner:

  for(int i: { 10, 2, 15, 28, 3 })

However, because of the limitations of deducing the type of the
initializer list in such range-based for expressions, that's not always
that simple, as in the second example above.

Even in such a simple case as this:

  unsigned values[] = { 1, 2, 3, 5 10 };

vs. this:

  for(unsigned value: { 1, 2, 3, 5, 10 })

if you turn on enough compiler warnings eg. gcc will warn about the
second one (converting 'int' to 'unsigned' may change the sign of the
result) but not the first one. I believe that in the first case the
compiler deduces the type of the initializer list to be 'unsigned'
(even though the literals themselves are of type 'int'), while in
the second case it does not.

I kind of grasp the difference between these two cases, but it just
makes range-based for loops less convenient when it's like this.

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initializer list type deduction rules Juha Nieminen <nospam@thanks.invalid> - 2022-08-09 07:54 +0000
  Re: initializer list type deduction rules Bo Persson <bo@bo-persson.se> - 2022-08-09 10:43 +0200
  Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-09 09:00 -0700
    Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-09 16:06 +0000
      Re: initializer list type deduction rules Juha Nieminen <nospam@thanks.invalid> - 2022-08-10 02:32 +0000
        Re: initializer list type deduction rules Paavo Helde <eesnimi@osa.pri.ee> - 2022-08-10 09:11 +0300
          Re: initializer list type deduction rules Juha Nieminen <nospam@thanks.invalid> - 2022-08-10 06:57 +0000
        Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-10 07:31 +0000
      Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-10 00:40 -0700
        Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-10 07:55 +0000
          Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-10 01:13 -0700
            Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-10 08:21 +0000
              Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-10 11:13 -0700
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-12 08:26 +0000
                Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-12 03:38 -0700
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-12 10:48 +0000
                Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-12 04:54 -0700
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-12 14:34 +0000
                Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-12 08:34 -0700
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-12 15:57 +0000
                Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-12 09:16 -0700
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-13 09:35 +0000
                Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-13 09:44 -0700
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-14 11:12 +0000
                Re: initializer list type deduction rules scott@slp53.sl.home (Scott Lurndal) - 2022-08-12 14:58 +0000
                Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-12 08:59 -0700
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-12 16:11 +0000
                Re: initializer list type deduction rules scott@slp53.sl.home (Scott Lurndal) - 2022-08-12 16:44 +0000
                Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-12 12:08 -0700
                Re: initializer list type deduction rules scott@slp53.sl.home (Scott Lurndal) - 2022-08-12 19:58 +0000
                Re: initializer list type deduction rules Öö Tiib <ootiib@hot.ee> - 2022-08-12 16:42 -0700
                Re: initializer list type deduction rules David Brown <david.brown@hesbynett.no> - 2022-08-13 18:14 +0200
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-14 11:06 +0000
                Re: initializer list type deduction rules David Brown <david.brown@hesbynett.no> - 2022-08-15 11:34 +0200
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-15 19:03 +0000
                Re: initializer list type deduction rules David Brown <david.brown@hesbynett.no> - 2022-08-15 21:23 +0200
                Re: initializer list type deduction rules red floyd <no.spam.here@its.invalid> - 2022-08-15 13:51 -0700
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-16 19:16 +0000
                Re: initializer list type deduction rules Paavo Helde <eesnimi@osa.pri.ee> - 2022-08-21 22:23 +0300
                Re: initializer list type deduction rules David Brown <david.brown@hesbynett.no> - 2022-08-22 08:08 +0200
                Re: initializer list type deduction rules Paavo Helde <eesnimi@osa.pri.ee> - 2022-08-22 11:37 +0300
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-22 10:23 +0000
          Re: initializer list type deduction rules Juha Nieminen <nospam@thanks.invalid> - 2022-08-11 06:24 +0000
            Re: initializer list type deduction rules Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-08-11 16:37 +0100
              Re: initializer list type deduction rules Juha Nieminen <nospam@thanks.invalid> - 2022-08-11 20:12 +0000
                Re: initializer list type deduction rules Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-08-12 00:09 +0100
                Re: initializer list type deduction rules Juha Nieminen <nospam@thanks.invalid> - 2022-08-12 11:51 +0000
            Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-12 08:29 +0000
              Re: initializer list type deduction rules Juha Nieminen <nospam@thanks.invalid> - 2022-08-12 12:08 +0000
                Re: initializer list type deduction rules Muttley@dastardlyhq.com - 2022-08-12 14:37 +0000
                Re: initializer list type deduction rules scott@slp53.sl.home (Scott Lurndal) - 2022-08-12 15:01 +0000
                Re: initializer list type deduction rules Juha Nieminen <nospam@thanks.invalid> - 2022-08-15 06:04 +0000
  Re: initializer list type deduction rules Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-08-09 16:08 -0700
    Re: initializer list type deduction rules Juha Nieminen <nospam@thanks.invalid> - 2022-08-10 02:34 +0000

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