Variables of struct and class types are called objects - discuss

[Jonathan M Davis]

On Sunday, August 3, 2025 5:29:46 AM Mountain Daylight Time Mike Parker via Digitalmars-d-learn wrote:
> Classes and structs in C++ are both value types, and instances of
> both are referred to as objects. This isn't unusual.
>
> An object is a concrete instance of a type described by a class
> or struct definition. It's the thing you're manipulating, not the
> definition. Whether you're manipulating it directly or through a
> reference makes no difference. Whether it's on the stack or the
> heap makes no difference.
>
> Consider that a pointer to a struct a reference to the struct
> instance in the same way a class variable is a reference to a
> class instance.

Exactly. I don't think that I've ever seen anyone claiming before that a
an instance of a struct should not be considered an object. An object is an
instance of any class or struct, and inheritance has nothing to do with it.

And really, the whole concept that D has with structs vs classes is somewhat
unique. C# has something similar (though IIRC, it's not quite the same),
whereas in C++, the only difference between a struct and a class is what the
default visibility level of its members are (public for structs and private
for classes). And from what I've seen, most languages have just gone with
classes. Glancing at Rust, it looks like they just went with structs, but
I'm not very familiar with Rust, so I don't know the details. But either
way, what exactly a class or struct is in a given language very much depends
on that language. Some of the concepts are pretty universal, but the details
can be quite different.

So, talking about structs vs classes in a general sense rather than when
talking about a specific language isn't very useful IMHO.

Similarly, you'll get arguments over whether inheritance is a core part of
object-oriented programming or not. Personally, I would have said that
having a struct or class which has member functions - and therefore
instances of that struct or class are objects with functions associated with
them - would be the core of what it means for object-oriented programming
and that inheritance was an extension of it and not a requirement, whereas
some people would argue that inheritance is a core requirement of
object-oriented programming. As I understand it, Smalltalk had a very
different form of object-oriented programming than what folks normally think
of today, and it was one of the first (if not the first) OO language, but
many folks these days think of Java's form form of OO when they think of OO,
which is probably why some folks think that OO must have inheritance in a
manner similar to Java.

And the reality of the matter is that pretty much every language uses such
terms in its own way which may or may not match what other languages use
those terms for. So, if you want to talking about a concept such as an
object or object-oriented programming, then you're going to tend to get a
lot of comparing and contrasting between languages, sometimes with someone
trying to claim that a particular language doesn't really qualify, because
it doesn't fit how they use the term (which was probably strongly influenced
by whichever languages they've used the most).

- Jonathan M Davis