Groups > comp.lang.c++ > #119588

Re: std::map::emplace useful in any way?

From	usenet@stegropa.de (Stefan Große Pawig)
Newsgroups	comp.lang.c++
Subject	Re: std::map::emplace useful in any way?
Date	2024-06-30 21:09 +0200
Organization	Dark Sky
Message-ID	<87jzi6gsct.fsf@ID-208667.user.individual.de> (permalink)
References	<v2t1pv$1bdc2$1@gwaiyur.mb-net.net>

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Marcel Mueller <news.5.maazl@spamgourmet.org> writes:
> The emplace functions generally allows to construct container objects
> directly at the target location. But std::map expects a value type of
> std::pair<const Key, T>. Now the implementation of emplace needs to
> instantiate the value type just to get the key to find the insert
> location. This cannot happen at the target location, isn't it?
>
> I know, this has been solved in C++17 by try_emplace. I just wonder what
> was the idea of this function.

While the value type may be instantiated and immediately destroyed when
it turns out that an element with the same key already exists, emplace()
still allows you to insert values that are neither copyable nor moveable.

  Stefan

Thread

std::map::emplace useful in any way? Marcel Mueller <news.5.maazl@spamgourmet.org> - 2024-05-25 17:57 +0200
  Re: std::map::emplace useful in any way? Paavo Helde <eesnimi@osa.pri.ee> - 2024-05-25 20:37 +0300
    Re: std::map::emplace useful in any way? Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-28 17:53 +0200
      Re: std::map::emplace useful in any way? Paavo Helde <eesnimi@osa.pri.ee> - 2024-05-29 11:11 +0300
        Re: std::map::emplace useful in any way? Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-29 11:47 +0200
          Re: std::map::emplace useful in any way? Paavo Helde <eesnimi@osa.pri.ee> - 2024-05-29 15:05 +0300
            Re: std::map::emplace useful in any way? Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-29 18:56 +0200
              Re: std::map::emplace useful in any way? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-05-29 12:23 -0700
                Re: std::map::emplace useful in any way? Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-30 16:01 +0200
  Re: std::map::emplace useful in any way? Bonita Montero <Bonita.Montero@gmail.com> - 2024-05-25 19:41 +0200
    Re: std::map::emplace useful in any way? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2024-06-30 09:47 -0700
      Re: std::map::emplace useful in any way? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-30 19:15 +0200
        Re: std::map::emplace useful in any way? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2024-06-30 11:46 -0700
        Re: std::map::emplace useful in any way? usenet@stegropa.de (Stefan Große Pawig) - 2024-06-30 21:21 +0200
          Re: std::map::emplace useful in any way? Bonita Montero <Bonita.Montero@gmail.com> - 2024-06-30 23:49 +0200
            Re: std::map::emplace useful in any way? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2024-06-30 18:29 -0700
              Re: std::map::emplace useful in any way? Bonita Montero <Bonita.Montero@gmail.com> - 2024-07-01 13:41 +0200
                Re: std::map::emplace useful in any way? Bonita Montero <Bonita.Montero@gmail.com> - 2024-07-07 13:17 +0200
                Re: std::map::emplace useful in any way? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2024-07-07 09:16 -0700
                Re: std::map::emplace useful in any way? Bonita Montero <Bonita.Montero@gmail.com> - 2024-07-07 18:18 +0200
            Re: std::map::emplace useful in any way? usenet@stegropa.de (Stefan Große Pawig) - 2024-07-01 07:41 +0200
  Re: std::map::emplace useful in any way? Sam <sam@email-scan.com> - 2024-05-25 18:29 -0400
  Re: std::map::emplace useful in any way? usenet@stegropa.de (Stefan Große Pawig) - 2024-06-30 21:09 +0200
  Re: std::map::emplace useful in any way? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2024-06-30 13:32 -0700
    Re: std::map::emplace useful in any way? Marcel Mueller <news.5.maazl@spamgourmet.org> - 2024-07-07 11:09 +0200

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