Creator: Completion no longer adds closing semicolon

sierdzio

@JonB said in Creator: Completion no longer adds closing semicolon:

Please don't shoot me for asking this here --- technically I guess it's OT --- but I have wondered (I'm not a C++-er): why does a C++ class X { ... } statement/construct actually need a terminating semi-colon?

There is no real reason. Somebody, somewhere, a long time ago, decided that this will be the syntax, and it stayed to this day ;-)

kshegunov

@sierdzio said in Creator: Completion no longer adds closing semicolon:

There is no real reason. Somebody, somewhere, a long time ago, decided that this will be the syntax, and it stayed to this day ;-)

I beg to disagree, @JonB's supposition is perfectly correct.

class {
} variable, *pointer;

is a valid and expected (in some cases) construct, albeit somewhat rare. So the semicolon has a well defined meaning and usage.

JonB

@kshegunov

Yes, I wondered whether C++ might allow just that, exactly as struct does! As you say, I have never seen that used with class! So, since we omitted even a class name after the word class, here we have an anonymous class. Interesting :)

kshegunov

There's no difference between struct and class in C++ with the exception of the default access specifier - being public and private respectively (also extending to default-access inheritance).

JonB

@kshegunov

There's no difference between struct and class in C++ with the exception of the default access specifier

Hmm, can I try to challenge this (without lazily just Googling!)?

One problem is that I'm used to C# not C++, C# has struct as well as class, but does have different semantics, so what I'm thinking of might be C# not C++...

IIRC (though I could be shaky!), in C# struct must have a constructor with no parameters, even if there is another overload which does take parameters. Not so for class. How's that in C++ ? :) In C++, class can do multiple inheritance, right? But structs can't multiple inherit, can they?

kshegunov

@JonB said in Creator: Completion no longer adds closing semicolon:

How's that in C++ ? :)

They're absolutely equivalent:

struct X
{
    X(int, int);
};

is the same as:

class X
{
public:
    X(int, int);
};

And then:

class X : Y
{
};

is the same as:

class X : private Y
{
};

as for struct:

struct X : Y
{
}:

is equivalent to:

struct X : public Y
{
};

Additionally inheritance can mix class and struct all the same, it doesn't care about the exact keyword you used, only cares about the access of each member.

But structs can't multiple inherit, can they?

Sure they can.

struct A { };
struct B { };
struct C : A, B  {};

Is absolutely valid.

JonB

@kshegunov

OK, this is why I like C & C# but not C++ ! I'll stop trying to think of where C++ struct might differ from class, since you're pretty clear & adamant that they don't :) Thanks.

sierdzio

@kshegunov said in Creator: Completion no longer adds closing semicolon:

class {
} variable, *pointer;

is a valid and expected (in some cases) construct, albeit somewhat rare

Indeed, point taken :-) You are right.

Asperamanca

@JonB said in Creator: Completion no longer adds closing semicolon:

@kshegunov

OK, this is why I like C & C# but not C++ ! I'll stop trying to think of where C++ struct might differ from class, since you're pretty clear & adamant that they don't :) Thanks.

C++ makes perfect sense, if you know it's history. Off the top of my head, I would say that struct came from pure C. When they designed C++, they needed a new construct for 'class', but decided to model it as closely as possible to an already existing construct, 'struct'. They decided that making everything public by default was too dangerous for 'class', but for compatibility reasons, they could not change that behavior for 'struct'.

Today, you can use 'struct' and 'class' to convey different intentions. See http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rc-struct

jsulm

@Asperamanca I think struct is still part of C++ because C should be a subset of C++ (more or less)

Asperamanca

@jsulm said in Creator: Completion no longer adds closing semicolon:

@Asperamanca I think struct is still part of C++ because C should be a subset of C++ (more or less)

I had no intention of saying "struct is not part of C++", because of course it is.

jsulm

@Asperamanca You misunderstood me: I think struct could be removed from C++ as it is redundant (class is same thing), but then C wouldn't be subset of C++ anymore.

Asperamanca

@jsulm
Compatibility to legacy code is one of the strengths of C++. I for one would not want to go digging in old but reliably working code, just because a new version of the language stopped supporting certain constructs.

When MS did that moving from VB6 to VB.NET, we dropped VB and since use C++ instead.

jsulm

@Asperamanca I didn't suggest to do it, just mentioned why (probably) C++ still has struct even if it has class.

JonB

@jsulm
C# has struct as well as class, even though it has no pretence of backward C compatibility!

And since we can't get C compilers any more, only C++ ones, thank goodness we can still get old-fashioned C code through them, without C++ bloatware ;-)

sierdzio

@JonB said in Creator: Completion no longer adds closing semicolon:

thank goodness we can still get old-fashioned C code through them,

... what? You make it sound like C compilers from clang, GCC etc. were now a byproduct of C++, kept only for compatibility. That's simply not the case. There's a ton of living C code out there which requires proper C compilers (C standard and C++ standard are not compatible) to compile and run. Linux kernel, to mention one example.

We're slowly drifting more and more off-topic in this conversation :-) Still, it's interesting.

I always thought that the semicolon after class is a dumb leftover, but it has been rightly pointed out that the old syntax is still supported, and that means the semicolon has to be there (otherwise the code would be ambiguous), it can't be removed. I'm happy to have read your arguments, guys, they made me think about it more :)

JonB

@sierdzio

https://en.wikipedia.org/wiki/GNU_Compiler_Collection:

In August 2012, the GCC steering committee announced that GCC now uses C++ as its implementation language.[30] This means that to build GCC from sources, a C++ compiler is required that understands ISO/IEC C++03 standard.

You need a C++ compiler just to produce a C compiler now! It's so sad... :(

aha_1980

For reference, the report is here: https://bugreports.qt.io/browse/QTCREATORBUG-19726

jsulm

@JonB Apparently even GCC developers do not want to use C
:-)
Next, Linux kernel developers will switch to C++ and use templates! :-)

mrjj

@jsulm
Naah as Linus would rather commit harakiri than use c++.