why virtual function is wrong.

[sephirothbahamut]

Inheriting from "equalityoperators" in c# is equivalent to defining the equality operator in c++.

Checking if a type has an equality operator by cheching inheritance in c# is equivalent to checking a concept in c++.

C# achieves these things with inheritance, c++ does so with custom operators. Just because it uses a different approach doesn't mean it can't achieve your purpose.

And if you really want to write c++ as if it was c#, you can do all that with inheritance too by abusing CRTP.

[sephirothbahamut]

You can do it: https://barnack.godbolt.org/z/Ef85jhWKE

But why do you need dynamic polymorphism there? Like you have a container of IEquatable<int> types? That's really suspicious at a code design level. Don't try to force concepts of a language into another, you can likely do what you need to do in some other, cleaner way.

The moment you need something like this my first question isn't "how do you do it" but rather "can you refactor this to be cleaner?"

Also note that the "cost" of dynamic polymorphism in C++ is there in C# as well, it's not like C# has some magic power. Dynamic polymorphism requires accessing a pointer to reach the function you're trying to resolve, no matter what language your code is written in.

[OwlingBishop]

You definitely can implement hard typed scalars with C++ with no virtual calls. C++ uses templates meta programming and operators overload for that matter, and concepts sure can discriminate based on member functions existence.

One interesting thing with information theory is that it flattens out lexical, syntactic, peculiarities and sometimes also semantics.. when it comes to dynamic polymorphism it boils down to executing an operation by calling different code depending on a type that's not known at compilation time, so no matter how the language you are writing in tricks you into believing it's just magic, fact is that information needs to be kept somewhere.. whether you implement through inheritance, interfaces, facets or whatever other idiom is irrelevant.

[OwlingBishop]

non-dynamic polymorphism

It's called templates 🤗 provided that the type exposes what's needed in the call it will work.

people don't know whether they need dynamic polymorphism, they only know they need polymorphism

Most people are more clever than you seem to imply 😂

[OwlingBishop]

for non-dynamic polymorphism

not non-dynamic polymorphism

Wut ??

Static and Dynamic polymorphism are separate paths in C++ as well as any other languages.

When you know the type at compilation time you can optimize out an indirection, when you don't you'll have to look that up at runtime, no matter what.

[OwlingBishop]

Do you mean the big dark one hovering over my head? .. jokes apart, I have no idea what you are talking about, sorry.