Comments on: How to implement the pimpl idiom by using unique_ptr

By: Jonathan Boccara

Jonathan Boccara — Sun, 21 Jan 2018 22:08:00 +0000

In reply to Peter Clarke. Ok, thanks for the info. Do you still have the error message at hand?

By: Peter Clarke

Peter Clarke — Mon, 15 Jan 2018 16:47:00 +0000

unique_ptr doesn’t seem to work for this method in Visual Studio 2017 but shared_ptr does.

By: Jonathan Boccara

Jonathan Boccara — Tue, 09 Jan 2018 21:23:00 +0000

In reply to Bartlomiej Filipek.

Thanks – Adding a link to your article: http://www.bfilipek.com/2018/01/pimpl.html

By: Bartlomiej Filipek

Bartlomiej Filipek — Fri, 05 Jan 2018 07:37:00 +0000

In reply to Jonathan Boccara.

it seems that purely virtual interfaces are a good alternative to pimpl.
here’s even a stackexchange question:

https://softwareengineering.stackexchange.com/questions/213259/whats-is-the-point-of-pimpl-pattern-while-we-can-use-interface-for-the-same-pur

so is anyone using pimpl? I know about QT with their d-ptr (like https://wiki.qt.io/D-Pointer) and Poco libs.

I’ve even asked a question at SO 🙂
https://stackoverflow.com/questions/48102705/where-is-pimpl-used-in-c-apps-libs-any-examples

By: Andy Saul

Andy Saul — Sun, 01 Oct 2017 15:51:00 +0000

Just a thought, but you don’t need to forward declare FridgeImpl in this case. Just use std::unique_ptr. As long as FridgeImpl derrives from Fridge, you can hide the whooe FridgeImpl class in the .cpp file

By: Aye Karlsson

Aye Karlsson — Mon, 25 Sep 2017 10:51:00 +0000

yeah i was looking for this a year ago and came across this : https://manu343726.github.io/2016/03/07/c++11-opaque-pointer-idiom.html

By: Jonathan Boccara

Jonathan Boccara — Sun, 24 Sep 2017 00:29:00 +0000

In reply to Andrew Jewell. Yes, that is the annoying thing with composition! Thanks for sharing your version to show another alternative to cut compilation dependencies.

By: Andrew Jewell

Andrew Jewell — Sun, 24 Sep 2017 00:08:00 +0000

In reply to Jonathan Boccara.

Yes, or add methods NewPlainFridge and NewFancyFridge, which provide alternate implementations, with no additional boilerplate code.

Mine also avoids the part that you omitted in your example, which is
void Fridge::coolDown() {impl_->coolDown();}
which is the part I find most annoying with the pimpl idiom.

By: Jonathan Boccara

Jonathan Boccara — Sat, 23 Sep 2017 20:03:00 +0000

In reply to Andrew Jewell.

So if I understand well it cuts compilation dependencies by using a interface and virtual methods as opposed to composition with the pimpl pointer.
To change the implementation, you then link with different file, that can define the method ‘NewFridge’ is that right?

By: Jonathan Boccara

Jonathan Boccara — Sat, 23 Sep 2017 20:00:00 +0000

In reply to XtoF. It's great if the article is helpful. Thanks for your comment!