Type Erasure

Type Erasure, a C++ specific design pattern, allows unrelated types to all be used by a single type. This video discusses what this pattern looks like, how it works, and some of the areas in the standard library where you will find it leveraged.
A special thanks to Nevin :-) Liber for teaching me everything I know on the subject.
A note about the video: I should have decayed the type in the assignment operator, or at least removed the reference. See pinned comment, below.

[@ferguswaugh80]

Hi, I'm a little new to universal references, so I may have some misunderstandings, but I'm fairly sure that the type 'T' in your Model is deduced as T& in the case of feeding the constructor an l-value. E.g. in this code snippet: godbolt.org/g/i12iR2 Is this deliberate? Or would something like this be better? godbolt.org/g/d3kdfx Really liking these videos by the way, covers some interesting C++ topics that I've found difficult to understand elsewhere, thanks for uploading :)

[@EverythingCpp]

Ahh, a fine catch! Yes, I should have decayed the type! m_value.reset(new Model(std::forward(value))); is what I should have put. I was careless with the universal reference... Am new to the KZbins, and now evaluating options to fix that...

[@EverythingCpp]

Though I believe the example, as is, deduces correctly. But for T&, it would be broken, storing a reference to the original, which is not intended.

[@BloodHaZaRd666]

@@EverythingCpp Didn't understand you rpoint of view? Could you explain further plz

[@AmirHosseinTamjidi]

I cannot emphasize how well prepared and clear this video was. Well done!

[@SuhailKhan-vr6ik]

Excellent video. Finally got an understanding of what we are trying to achieve with type erasure and how we do it.

[@stephenhowe4107]

I like what you present. Very helpful. Just for the sake of completeness, you might like to say, why would you want to do type erasure - what are the benefits? What do you gain? And also what do you lose (but the video mentions some of the downsides)? It is important that the programmer knows all of these so they can say to themselves, "yes I am going to use type erasure in the code here" or "because of these downsides and code requirements, I am not going to use type erasure". std::any is reaching towards a C++ version of C's union. I have seen Alexandrescu's discriminated union code (mentioned in Herb Sutter's books). And also, what, if any, are there of alternative ways of implementing type erasure? It is important that various ways of doing C++ patterns are documented, the pluses and minuses of each technique and what problem they attempt to solve.

[@ekremvkilic]

The return *this in operator overload of assignment is missing. Also, it is better to define Move Constructor for Model struct and move the passed object along the way. Besides that, the video is great. Thanks!

[@p.polunin]

Thank you very much for such a clear explanation!

[@TheTemplarofAnubis]

Some applications and use case examples would help so much with your videos.

[@yomoma6692]

Tanks, that helped quite a bit.

[@Bbdu75yg]

Brilliant ❤ , thank you so much !

[@xiaobaibai5871]

great idea, thanks

[@muhdiversity7409]

This video just proves that C++ jumped the shark long ago. Where most of your effort is fighting C++ syntax/complexity and becoming a language lawyer as opposed to writing simple code that does something useful.

[@yyoud88]

Don't you need to use `std::move(value)` in ctor and move assignment of `TypeErased`?

[@MaitreBart]

I think the proper handler would be std::forward().

[@yyoud88]

I don’t think so. Search copy-and-move clang tidy.

[@R_BNK]

Very nice explanation...👍