Better Code: Runtime Polymorphism - Sean Parent 

"My class inherits from nothing." This is my favorite dev video of all time.

42:20 JUST DO IT ! Don't let your dreams be dreams ! Love this talk, Sean Parent is awesome as always.

You must execute epic feats of complex and subtle language kung fu to beat C++ into semantic submission.

I have been using this pattern for the past 5 years now. It uses so little boilerplate for what it achieves. I learned to apply similar techniques all over my code.

Great talk! The only thing I'd disagree with is that mutable polymorphic objects are an extreme exception. In my experience, they are rather common. For example, imagine an abstract base class for an audio plugin with a process() method. Each concrete plugin would override the process() method to implement their DSP algorithm. This method must be non-const because some plugins need to maintain and mutate state, e.g. a filter or delay line. The host application, however, doesn't care about the implementation details, it just wants to process audio buffers by passing them to the process() method of each plugin in a particular order.

His voice is very calming

Amazing how similar the talk is to the one in 2011 and still it's more relevant that ever!

At some point this started to remind of the old meme "yo dawg I heard you liked documents so I put your document inside your document"

I could watch this talk every day.

Excellent! I will watch this again. Thanks.

This guy codes! Great talk!

Great talk and a great pattern. Small code improvement: instead of assert(x.size()) use assert(!x.empty()) - it is more clear about the intent and does not require the container to know or compute its size (linked lists size() can be O(n) but empty() is O(1)).

Thanks for the great talk! Just wanted to add that the description is a bit misleading: there is inheritance involved. It is just hidden from the library user and done automatically "on use" through a template.

Great Talk!

@29:44 -- I'm running the same code with C++17 gcc 5.4.0 and I don't get the copy constructor call. I only get the two ctor calls. So that issue with the compiler deleting the default copy/move assignment for classes with non-static data members or direct base classes NOT defining a move assignment operator appears to be mitigated.

Reminds me of common lisp's generic functions -- (defmethod draw (obj) ... ) -- nice talk!

@49:22 This is not a demonstration that the copy constructor isn't still being called many times. Since you deleted the explicit copy constructor instrumented to print "Copy", you didn't need to make any of the other changes to have the same output. There is no way to see if the implicitly compiler-generated copy constructor is still being called. Not sure how to make an actual, proper demonstration of success; when I add an instrumented copy back in, it is indeed still disappointingly being called many times.

WOW!! I'd say this is a *very big* part of a concept to solve "modern problems with OOP" regarding multithreading performance - since polymorphism (as one of THE most valuable features of OOP!) comes with all different kinds of drawbacks, usually. :-) Thanks for this inspirational presentation!

I wanna like this more than once

Didn't we lose the equality semantics of a regular type for the `int` wrapper class at 21:00? If I copy an object and check for equality it would return false cause the `unique_ptr`s would point to different objects.

If you resize a photoshop document, does that reset the history? Wouldn't the sparse tile system get confused?

I think I'm missing something obvious at 46:57, there is 2 objects in the document when he commit(), but there's 4 copies. Why is there 4 copies not 2?

Is there any place on the web where I can find the final code? There is no slide in this vid that shows the whole thing on one screen.

He is a wizard

at around 7:20, if emplace_back fails to allocate memory, doesn't that mean we're out of RAM and we have bigger problems than leaking memory because the program is about to crash anyways.

@25:52 It looks like a copy-and-swap idiom. Why we use move (and move assignment) here instead of using swap for selfs?

Any textual description of the talk?

What happens to Photoshop's undo history if I use a filter globally on a huge document? Sparse tiling won't help.

Here are the slides: sean-parent.stlab.cc/presentations/2017-01-18-runtime-polymorphism/2017-01-18-runtime-polymorphism.pdf

Basically Rust traits but more boilerplate. Gotchu.

Can someone explain me why do we need the abstract virtual base struct concept_t ? Concept struct is used by the Type Copy Assignment function. Since the compiler would write the copy assignment function for every type that we use do we need another indirection.

Trying to understand this. How is it different from the pimpl idiom? ...

38:08 he says there are potential performance gains because you don't have to wrap strings or ints in a class. Yet that's exactly what he's doing under the hood. Seems to me if I wrote a wrapper class for int or string with all his little copy/move optimizations, it would be the same code for all intents and purposes. Maybe more convenient for a library consumer to code against, but no different performance-wise. What am I missing? I'd love to see some benchmarks on the two coding styles.

Explanation of incidental data structure did not make any sense to me.

I'm sorry, but I'm not seeing it. You say at 38:00 that you don't need to wrap your ints or strings into objects, but don't you wrap them anyway (model)? You just hide it from the client.

5 people audience?

52:18 - neither Go or Swift goes anywhere near or as far as Rust when it comes to polymorphic value types.

Why not delete the copy constructor and define the move constructor? Isn’t it kind of dishonest to say that this is a copy when its a move.

Quantify "indirection, heap allocation, and virtualization impact my performance"... by how much? 1 nanosecond? Is it more than adding two integers together? Do we analyze the performance of addition and subtraction? I don't understand why everyone is so dogmatic about these things unless they actually have constraints where they are doing something that has to run in 100ns or on 16k of memory. .. and sure those situations exist, but I am getting really tired of talking about a few nanoseconds of performance while we are waiting a full second for a user to click a button. How many cpu cycles does it really take to allocate an object? and don't you only allocate it once? How many cpu cycles does indirection take up? one? five?

2:36 what is inheritance

At 38:06. It's not true. You do have to wrap integers and strings into objects. This is what object_t is. Btw, it's the same technique std::shared_ptr uses to store custom deleters. The basic idea of the rest of the code is how to use function overloading for polymorphism.

6:11 "how many people see the bug?" ... Me: WHAT!? BUG?!?!?!?!!?!?

Yeah, Photoshop is just so slow that I can't even see how can someone use it as an example of optimized software.

C++ could be so much easier if the language would implement free function overload and polymorphism on more then just the first argument (the implicit this argument) like CLOS (the lisp object system). This is exactly what this concept classes do by foot. But hey maybe we get this in C++44. Glaciers move faster then this language comittee.

This class document looks like xml ...but it would be better if it was protobuf :D