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Inheritance was invented as a performance hack (2021)

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Re: Inheritance was invented as a performance hack (2021)

#31

Post by nine_k »

xxs wrote: post #21
nine_k wrote: post #16

Earlier quoted context omitted.

This assumes that the vtables stay in at least L2 cache, which may be a correct assumption for the few hot-path classes. In this regard, I remember how Facebook's android app once failed to build when the codebase exceeded the limit of 64k classes.

No, Java does Class hierarchy analysis and has multiple way not to use v-table calls. Single site (no class found overriding a method) are static and can be inlined directly. Dual call sites use a class check (which is a simple equality), can be inlined, no v-table. 3-5 call sites use inline caches (e.g. the compiler records what class have been used) that are similar and some can be inlined, usually plus a guard che…

Thanks, TIL!

Re: Inheritance was invented as a performance hack (2021)

#32

Post by ninetyninenine »

roenxi wrote: post #10

I'm not sold the evidence is there to show inheritance is a good idea - it basically says that constructors, data storage and interfaces need to be intertwined. That isn't a very powerful abstraction, because they don't need to be and there isn't an obvious advantage from doing so over picking up the concepts separately as required. And inheritance naturally suggests grouping interfaces into a tree in the way that se…

It is a good idea because it's the most fundamental idea.

You have two objects. A and B. How do you merge the two objects? A + B?

The most straight forward way is inheritance. The idea is fundamental.

The reason why it's not practical has more to do with human nature and the limitations of our capabilities in handling complexity then it has to do with the concept of inheritance itself.

Literally think about it. How else do you merge two structs if not using inheritance?

The idea that inheritance is not fundamental and is wrong in nature is in itself mistaken.

Re: Inheritance was invented as a performance hack (2021)

#34

Post by rakejake »

IMHO Inheritance (especially the C++ flavored inheritance with its access specifiers and myriad rules) has always scared me. It makes a codebase confusing and hard to reason with. I feel the eschewing of inheritance by languages such as Go and Rust is a step in the right direction.

As an aside, I have noticed that the robotics frameworks (ROS and ROS2) heavily rely on inheritance and some co-dependent C++ features like virtual destructors (to call the derived class's destructor through a base class pointer). I was once invited to an interview for a robotics company due to my "C++ experience"and grilled on this pattern of C++ that I was completely unfamiliar with. I seriously considered removing C++ from my resume that day.

Re: Inheritance was invented as a performance hack (2021)

#35

Post by int_19h »

DaiPlusPlus wrote: post #22
echelon wrote: post #18

Earlier quoted context omitted.

Rigid, "family tree"-style inheritance as in classical OOP is pretty much garbage. "A cow is a mammal is an animal" is largely useless for the day to day work we do except in extremely well-planned, large and elaborate ontologies -- something you typically only see in highly structured software like windowing systems. It just isn't useful for the majority of our work. "Trait/Typeclass"-style compositional inheritance…

> "Trait/Typeclass"-style compositional inheritance as in Rust and Haskell is sublime. It's similar to Java interfaces in terms of flexibility, and it doesn't enforce hierarchical rules. Yes-and-no. Interfaces still participate in inheritance hierarchies (`interface Bar extends Foo`), and that's in a way that prohibits removing/subtracting type members (so interfaces are not in any way a substitute for mixins). Compo…

How are interfaces with ability to provide default implementations for members (which both C# and Java allow today) not a substitute for mixins?

"Only reference types can implement interfaces" is simply not true in C#. Not only can structs implement them, but they can also be used through the interface without boxing (via generics).

Re: Inheritance was invented as a performance hack (2021)

#36

Post by josephg »

osigurdson wrote: post #28
roenxi wrote: post #10

I'm not sold the evidence is there to show inheritance is a good idea - it basically says that constructors, data storage and interfaces need to be intertwined. That isn't a very powerful abstraction, because they don't need to be and there isn't an obvious advantage from doing so over picking up the concepts separately as required. And inheritance naturally suggests grouping interfaces into a tree in the way that se…

Yeah ya... everyone likes to go on and on about how inheritance is the root of all evil and if you just don't use it, everything will be fine. Sorry, it won't be fine. Your software will still be a mess unless it is small and written three times by the same person who knows what they are doing. The bottom line is, no one ever really used inheritance that much anyway (other than smart people trying to outsmart themsel…

> The bottom line is, no one ever really used inheritance that much anyway

If you think that, you have no idea how much horrible code is out there. Especially in enterprise land, where deadlines are set by people who get paid by the hour. I once worked on a java project which had a method - call a method - call a method - call a method and so on. Usually, the calls were via some abstract interface with a single implementor, making it hard to figure out what was even being executed. But if you kept at it, there were 19 layers before the chain of methods did anything other than call the next one. There was a separate parallel path of methods that also went 19 layers deep for cleaning up. But if you follow it all the way down, it turns out the final method was empty. 19 methods + adjacent interface methods all for a no-op.

> The bottom line is, most people don't have any original opinions at all and are just going with whatever seems to be popular.

Most people go with the crowd. But there's a reason the crowd is moving against inheritance. The reason is that inheritance is almost always a bad idea in practice. And more and more smart people talking about it are slowly moving sentiment.

Bit by bit, we're finally starting to win the fight against people who think pointless abstraction will make their software better. Thank goodness - I've been shouting this stuff from the rooftops for 15+ years at this point.

Re: Inheritance was invented as a performance hack (2021)

#38

Post by codr7 »

roenxi wrote: post #10

I'm not sold the evidence is there to show inheritance is a good idea - it basically says that constructors, data storage and interfaces need to be intertwined. That isn't a very powerful abstraction, because they don't need to be and there isn't an obvious advantage from doing so over picking up the concepts separately as required. And inheritance naturally suggests grouping interfaces into a tree in the way that se…

But they're not building trees, that's how inheritance is mostly used today.

After reading this, I'm thinking that intrusive lists is the one use of inheritance in C++ that makes any sense.

Re: Inheritance was invented as a performance hack (2021)

#39

Post by josephg »

ninetyninenine wrote: post #32
roenxi wrote: post #10

I'm not sold the evidence is there to show inheritance is a good idea - it basically says that constructors, data storage and interfaces need to be intertwined. That isn't a very powerful abstraction, because they don't need to be and there isn't an obvious advantage from doing so over picking up the concepts separately as required. And inheritance naturally suggests grouping interfaces into a tree in the way that se…

It is a good idea because it's the most fundamental idea. You have two objects. A and B. How do you merge the two objects? A + B? The most straight forward way is inheritance. The idea is fundamental. The reason why it's not practical has more to do with human nature and the limitations of our capabilities in handling complexity then it has to do with the concept of inheritance itself. Literally think about it. How e…

> Literally think about it. How else do you merge two structs if not using inheritance?

What? Using multiple inheritence? That's one of the worst ideas I've ever seen in all of computer science. You can't just glue two arbitrary classes together and expect their invariants to somehow hold true. Even if they do, what happens when both classes implement a method or field with the same name? Bugs. You get bugs.

I've been programming for 30 years and I've still never seen an example of multiple inheritance that hasn't eventually become a source of regret.

The way to merge two structs is via composition:

    struct C {
        a: A,
        b: B,
    }
If you want to expose methods from A or B, either wrap the methods or make the a or b fields public / protected and let callers call c.a.foo().

Don't take my word for it, here's google's C++ style guide[1]

> Composition is often more appropriate than inheritance.

> Multiple inheritance is especially problematic, because it often imposes a higher performance overhead (in fact, the performance drop from single inheritance to multiple inheritance can often be greater than the performance drop from ordinary to virtual dispatch), and because it risks leading to "diamond" inheritance patterns, which are prone to ambiguity, confusion, and outright bugs.

> Multiple inheritance is permitted, but multiple implementation inheritance is strongly discouraged.

[1] https://google.github.io/styleguide/cppguide.html#Inheritanc...

Re: Inheritance was invented as a performance hack (2021)

#40

Post by rixed »

osigurdson wrote: post #28
roenxi wrote: post #10

I'm not sold the evidence is there to show inheritance is a good idea - it basically says that constructors, data storage and interfaces need to be intertwined. That isn't a very powerful abstraction, because they don't need to be and there isn't an obvious advantage from doing so over picking up the concepts separately as required. And inheritance naturally suggests grouping interfaces into a tree in the way that se…

Yeah ya... everyone likes to go on and on about how inheritance is the root of all evil and if you just don't use it, everything will be fine. Sorry, it won't be fine. Your software will still be a mess unless it is small and written three times by the same person who knows what they are doing. The bottom line is, no one ever really used inheritance that much anyway (other than smart people trying to outsmart themsel…

I believe you just summed up 90% of popular wisdom about software engineering.

With enough patience you will see many fads pass twice like a tide raising and falling. OOP, runtime typing, schema-less databases and TDD are the first to come to mind.

I feel "self-describing" data formats and everything agile are fading already.

Very few ideas stick, but some do: I do not expect GOTO to ever come back, but who knows where vibe coding will lead us :)

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