Base struct instead of class

[Ron Natalie]

Re: Base struct instead of class


"White Wolf" <wolof@freemail .hu> wrote in message news:bjenr4$o7t $1@phys-news1.kolumbus. fi...
[color=blue]
> First: *all* of your classes *must* have a virtual destructor. They all
> have virtual functions. Especially hashable and runnable *must* have
> virtual destructors.[/color]

Not necessarily true. Do not confuse "rules of thumb" with the MUST rules
of the language. The only time you need a virtual destructor is when derived
classes are deleted through pointers of their base types.

[Mike Smith]

Re: Base struct instead of class

Alf P. Steinbach wrote:[color=blue]
>
> Thanks, and please pass the word (it's September again).[/color]

Isn't it always? ;-)

--
Mike Smith

[Mike Smith]

Re: Base struct instead of class

Ivan Vecerina wrote:[color=blue]
>
> As Thomas mentioned, this only saves you from having to add
> a 'public:' specification. Except for the public access
> specifications, all uses of keyword 'struct' can be relaced
> by 'class' in C++.[/color]

Or vice versa - one could argue that the "class" keyword was never
necessary at all, whereas "struct", of course, was already pre-existing
in C.

--
Mike Smith

[Dave Theese]

Re: Base struct instead of class

[color=blue][color=green]
> > As Thomas mentioned, this only saves you from having to add
> > a 'public:' specification. Except for the public access
> > specifications, all uses of keyword 'struct' can be relaced
> > by 'class' in C++.[/color][/color]

Actually, there is one other thing to look out for...

When inheriting, if you don't specify public, inherited or private, the
default will be different depending on whether you inherit from a struct or
class. When inheriting from a struct, it will be public inheritance; when
inheriting from a class, it will be private inheritance.

So, if you replaced all "struct"s with "class"es and added "public" access
specifications as necessary to make all access rights equivalent to what
they were before, it is still possible for the meaning of a program to
change. Specifically, some public inheritance might change to private
inheritance, as stated above...

[jeffc]

Re: Base struct instead of class


"Mike Smith" <mike_UNDERSCOR E_smith@acm.DOT .org> wrote in message
news:vls8iofm75 sg39@news.super news.com...[color=blue]
>
> Or vice versa - one could argue that the "class" keyword was never
> necessary at all, whereas "struct", of course, was already pre-existing
> in C.[/color]

Or, since the meaning of struct has changed from C, one could argue that
struct shouldn't do anything different from what it did in C, but only the
new keyword class should be used to implement classes.

[Ron Natalie]

Re: Base struct instead of class

Dave Theese wrote:
[color=blue]
>
> When inheriting, if you don't specify public, inherited or private, the
> default will be different depending on whether you inherit from a struct or
> class. When inheriting from a struct, it will be public inheritance; when
> inheriting from a class, it will be private inheritance.[/color]

No, it doesn't work that way. It doesn't matter whether the class you are
inheritting from was defined with struct or class. What matters is the key
used to define the derived class.

struct X; // or class X; it doesn't matter

struct Y : X { } ; // Public inheritance
class Y : X { } ; // Private inheritance.
[color=blue]
>
> So, if you replaced all "struct"s with "class"es and added "public" access
> specifications as necessary to make all access rights equivalent to what
> they were before, it is still possible for the meaning of a program to
> change. Specifically, some public inheritance might change to private
> inheritance, as stated above...[/color]

Nope, you just have to make sure you put in enough public keys

struct Y : X { ...
is equivielent to
class Y : public X {
public: ...

[Default User]

Re: Base struct instead of class

Mike Smith wrote:[color=blue]
>
> Alf P. Steinbach wrote:[color=green]
> >
> > Thanks, and please pass the word (it's September again).[/color]
>
> Isn't it always? ;-)[/color]


Yes, but sometimes it's more September than other times. Like in
September.




Brian Rodenborn

[Dave Theese]

Re: Base struct instead of class

> > When inheriting, if you don't specify public, inherited or private, the[color=blue][color=green]
> > default will be different depending on whether you inherit from a struct[/color][/color]
or[color=blue][color=green]
> > class. When inheriting from a struct, it will be public inheritance;[/color][/color]
when[color=blue][color=green]
> > inheriting from a class, it will be private inheritance.[/color]
>
> No, it doesn't work that way. It doesn't matter whether the class you[/color]
are[color=blue]
> inheritting from was defined with struct or class. What matters is the[/color]
key[color=blue]
> used to define the derived class.
>
> struct X; // or class X; it doesn't matter
>
> struct Y : X { } ; // Public inheritance
> class Y : X { } ; // Private inheritance.
>[color=green]
> >
> > So, if you replaced all "struct"s with "class"es and added "public"[/color][/color]
access[color=blue][color=green]
> > specifications as necessary to make all access rights equivalent to what
> > they were before, it is still possible for the meaning of a program to
> > change. Specifically, some public inheritance might change to private
> > inheritance, as stated above...[/color]
>
> Nope, you just have to make sure you put in enough public keys
>
> struct Y : X { ...
> is equivielent to
> class Y : public X {
> public: ...[/color]

Oh geez, you are absolutely right. Public vs. private by default depends on
the derived class, not the base class. 11.2.2 spells this out...

Thx for setting it straight!