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by neverartful 1975 days ago
The fact that you can swizzle methods also says a lot about its power and flexibility. When Steve Jobs was at NeXT, he was quoted numerous times bashing C++ as having 'dead objects' while pointing out that ObjC objects were 'alive'. One seldom needs to make use of swizzling, but when you do need it, it's an awesome capability.

As prabhatjha pointed out in another comment in this thread, swizzling was used to automatically capture networking calls just by adding our framework to your app and initializing it. You could then log into our app's web-based dashboard and see stats about networking calls (counts, latency, errors, etc.). This simple and elegant solution would not have been possible with C++. We also supported Android at the time (Java), and the developer was required to change his code to call our networking wrapper calls to get the same tracking for their Android apps.
2 comments
PaulDavisThe1st 1975 days ago
Absolutely. I've used swizzling myself to fix issues with audio plugin's GUIs (to limit how fast they are allowed to redraw themselves). It's very clever and sometimes very useful.

But the ability to do that comes with certain costs, and performance is one of them. The fact that these "methods" are dynamically dispatched sometimes matters, and you can't change that any more than you can swizzle in C++.

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PaulDavisThe1st 1974 days ago
> This simple and elegant solution would not have been possible with C++

Actually, it would, but not via any feature of the language. You can use features of the linker to accomplish this (particularly LD_PRELOAD). It's not the same thing, really, but it felt worth mentioning for the record.

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neverartful 1974 days ago
In our case, the LD_PRELOAD approach would not have worked because this was on iOS devices where you can't set that variable. However, I do appreciate you mentioning it because it too is a powerful mechanism that enables some creative and non-invasive solutions in some cases.
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pjmlp 1974 days ago
Here is how to do it in Windows.

https://www.microsoft.com/en-us/research/project/detours/

https://github.com/microsoft/Detours

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