Using automatic object deconstruction as Library Initialization and Cleanup

Question

The idea of using the automatic object deconstruction of Stack allocated objects got me thinking of using the system as a way to initialize and clean up 3rd party libraries.

Example:

#include <libA.h>
#include <libB.h>

namespace library {
 class Wrapper {
    Wrapper() {
         libA_init();
         libB_init();
    }
     ~Wrapper() {
        libB_exit();
        libA_exit();
     }
  }
}
int main() {
    library::Wrapper library;

}

People already argued on SO if the simple use of automatic stack deallocation should be called RAII as RAII withouth the R is simply the way OO works. (Allocation is initialization? Sounds like calling a constructor to me.)

Is this usage a well known antipattern or a good idea to organise code?

The term to look up is RAII. And you just stumbled into what is IMO the most important feature and pattern of C++. — StoryTeller - Unslander Monica, Jan 08 '19 at 08:21
... that is why I tagged it as RAII ... The question is rather: "Should I (mis)use this basic RAII pattern for something that is not a (meta)physical resource?" — salbeira, Jan 08 '19 at 08:23
So you know the term, and you ask instead of reading the plethora of material on why C++ programs should do this? — StoryTeller - Unslander Monica, Jan 08 '19 at 08:25
And no, it's not the question. Don't expect us to read your mind, be explicit. — StoryTeller - Unslander Monica, Jan 08 '19 at 08:25
As `libA_init()` is a call that probably initializes some global state, you should make your wrapper an singleton. — KamilCuk, Jan 08 '19 at 08:26
Sorry I thought the formulation of my question and the fact I already tagged it as a RAII question gives the fact I am not looking for explanations of what RAII is away. Especially since I did some research beforehand and found people screaming at others for calling the use of stack deallocation RAII in general. — salbeira, Jan 08 '19 at 08:34
Well, it's not formulated clearly. Since SO is all about being specific, you should be too. It makes it easier to answer and prevents shifting goalposts syndrome. I don't think your intended question is without merit, but it needs to be posed clearly. — StoryTeller - Unslander Monica, Jan 08 '19 at 08:38

score 2 · Answer 1 · answered Jan 08 '19 at 08:35

2

You asked :

Is this a well known antipattern or a good idea to organise code?

A good idea. Since it's a ressource managing problem, it's a really clean and neat way of organizing 3rd. party c-style library init/cleanup and one I have seen and used before.

Although there are a few finer points to your example.

First, having more than one in each class, clearly breaks with the "one class one responsibility" principle.

Second, unless theres a good reason not to, the init should be placed outside of main (for example, directly following the class definition).

answered Jan 08 '19 at 08:35

darune

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Would placing the initialization as global objects not break my control over when which library gets initialized (like when multiple depend on each other like first initializing glfw for OpenGL, then creating a glfw window that's need to be made current to then initialize the GLAD library to load function pointers etc. etc.) – salbeira Jan 08 '19 at 08:44
@salbeira it would and then you may have a reason and be fine with having the code run in main, however there exists other solutions particular to this problem (ie. controlling "static initialization order"). – darune Jan 08 '19 at 08:47
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As long as all the different objects depending one on another are defined in the same compilation unit, order of initialisation is the order of definition! You only risk trouble if you distribute the objects over different compilation units. – Aconcagua Jan 08 '19 at 09:09

πάντα ῥεῖ · Answer 2 · 2019-01-08T08:24:46.607

0

Is this a well known antipattern or a good idea to organise code?

Totally depends on the scope you need to do that.

In general RAII isn't an antipattern, but the preferred pattern to use with c++.

You probably need to take care of the automatically generated copy constructors and assignment operators for library::Wrapper and you may delete those explicitly.

edited Jan 08 '19 at 08:24

answered Jan 08 '19 at 08:20

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I wasn't sure if I can call the use of automatic stack object deconstruction RAII in general. – salbeira Jan 08 '19 at 08:23
@salbeira It's the common usage, don't worry. – πάντα ῥεῖ Jan 08 '19 at 08:26

Using automatic object deconstruction as Library Initialization and Cleanup

2 Answers2