Walter

How hard would it be to add a (non-default, I suppose) flag (-wxs) to warn
when catching by value for non-fundamental, or for non-POD, types, as in:

class A
{};

class B
  : public A
{};

try
{
  throw B()
}
catch(A a) // "Warning: Catch clause type is by value for polymorphic type"
{

}

It'd be sweet (and would get DMC++ a special mention in Part 5, which I may
do next).

Matthew

It's not so easy to tell that a class has been derived from, such as if class B is in another file.

"Matthew Wilson" <matthew@stlsoft.org> wrote in message news:bhpg7o$1sfb$1@digitaldaemon.com...
> Walter
>
> How hard would it be to add a (non-default, I suppose) flag (-wxs) to warn
> when catching by value for non-fundamental, or for non-POD, types, as in:
>
> class A
> {};
>
> class B
>   : public A
> {};
>
> try
> {
>   throw B()
> }
> catch(A a) // "Warning: Catch clause type is by value for polymorphic
type"
> {
>
> }
>
> It'd be sweet (and would get DMC++ a special mention in Part 5, which I
may
> do next).
>
> Matthew
>
>

I appreciate that, but surely it's possible to readily deduce that a non-POD type is being caught by value?

"Walter" <walter@digitalmars.com> wrote in message news:bi1l46$1lbs$4@digitaldaemon.com...
> It's not so easy to tell that a class has been derived from, such as if class B is in another file.
>
> "Matthew Wilson" <matthew@stlsoft.org> wrote in message news:bhpg7o$1sfb$1@digitaldaemon.com...
> > Walter
> >
> > How hard would it be to add a (non-default, I suppose) flag (-wxs) to
warn
> > when catching by value for non-fundamental, or for non-POD, types, as
in:
> >
> > class A
> > {};
> >
> > class B
> >   : public A
> > {};
> >
> > try
> > {
> >   throw B()
> > }
> > catch(A a) // "Warning: Catch clause type is by value for polymorphic
> type"
> > {
> >
> > }
> >
> > It'd be sweet (and would get DMC++ a special mention in Part 5, which I
> may
> > do next).
> >
> > Matthew
> >
> >
>
>

What's a POD?

"Matthew Wilson" <matthew@stlsoft.org> wrote in message news:bi1piu$1rrj$1@digitaldaemon.com...
> I appreciate that, but surely it's possible to readily deduce that a
non-POD
> type is being caught by value?
>
> "Walter" <walter@digitalmars.com> wrote in message news:bi1l46$1lbs$4@digitaldaemon.com...
> > It's not so easy to tell that a class has been derived from, such as if class B is in another file.
> >
> > "Matthew Wilson" <matthew@stlsoft.org> wrote in message news:bhpg7o$1sfb$1@digitaldaemon.com...
> > > Walter
> > >
> > > How hard would it be to add a (non-default, I suppose) flag (-wxs) to
> warn
> > > when catching by value for non-fundamental, or for non-POD, types, as
> in:
> > >
> > > class A
> > > {};
> > >
> > > class B
> > >   : public A
> > > {};
> > >
> > > try
> > > {
> > >   throw B()
> > > }
> > > catch(A a) // "Warning: Catch clause type is by value for polymorphic
> > type"
> > > {
> > >
> > > }
> > >
> > > It'd be sweet (and would get DMC++ a special mention in Part 5, which
I
> > may
> > > do next).
> > >
> > > Matthew
> > >
> > >
> >
> >
>
>

Plain Old Data. Stuff with ctors/dtors/copy-assignment ops/etc.

I'm pretty sure it's defined in the standard. I'll have a look.

"Walter" <walter@digitalmars.com> wrote in message news:bi4cq6$2n5h$1@digitaldaemon.com...
> What's a POD?
>
> "Matthew Wilson" <matthew@stlsoft.org> wrote in message news:bi1piu$1rrj$1@digitaldaemon.com...
> > I appreciate that, but surely it's possible to readily deduce that a
> non-POD
> > type is being caught by value?
> >
> > "Walter" <walter@digitalmars.com> wrote in message news:bi1l46$1lbs$4@digitaldaemon.com...
> > > It's not so easy to tell that a class has been derived from, such as
if
> > > class B is in another file.
> > >
> > > "Matthew Wilson" <matthew@stlsoft.org> wrote in message news:bhpg7o$1sfb$1@digitaldaemon.com...
> > > > Walter
> > > >
> > > > How hard would it be to add a (non-default, I suppose) flag (-wxs)
to
> > warn
> > > > when catching by value for non-fundamental, or for non-POD, types,
as
> > in:
> > > >
> > > > class A
> > > > {};
> > > >
> > > > class B
> > > >   : public A
> > > > {};
> > > >
> > > > try
> > > > {
> > > >   throw B()
> > > > }
> > > > catch(A a) // "Warning: Catch clause type is by value for
polymorphic
> > > type"
> > > > {
> > > >
> > > > }
> > > >
> > > > It'd be sweet (and would get DMC++ a special mention in Part 5,
which
> I
> > > may
> > > > do next).
> > > >
> > > > Matthew
> > > >
> > > >
> > >
> > >
> >
> >
>
>

3.9

"Matthew Wilson" <dmd@synesis.com.au> wrote in message news:bi4cta$2n97$1@digitaldaemon.com...
> Plain Old Data. Stuff with ctors/dtors/copy-assignment ops/etc.
>
> I'm pretty sure it's defined in the standard. I'll have a look.
>
> "Walter" <walter@digitalmars.com> wrote in message news:bi4cq6$2n5h$1@digitaldaemon.com...
> > What's a POD?
> >
> > "Matthew Wilson" <matthew@stlsoft.org> wrote in message news:bi1piu$1rrj$1@digitaldaemon.com...
> > > I appreciate that, but surely it's possible to readily deduce that a
> > non-POD
> > > type is being caught by value?
> > >
> > > "Walter" <walter@digitalmars.com> wrote in message news:bi1l46$1lbs$4@digitaldaemon.com...
> > > > It's not so easy to tell that a class has been derived from, such as
> if
> > > > class B is in another file.
> > > >
> > > > "Matthew Wilson" <matthew@stlsoft.org> wrote in message news:bhpg7o$1sfb$1@digitaldaemon.com...
> > > > > Walter
> > > > >
> > > > > How hard would it be to add a (non-default, I suppose) flag (-wxs)
> to
> > > warn
> > > > > when catching by value for non-fundamental, or for non-POD, types,
> as
> > > in:
> > > > >
> > > > > class A
> > > > > {};
> > > > >
> > > > > class B
> > > > >   : public A
> > > > > {};
> > > > >
> > > > > try
> > > > > {
> > > > >   throw B()
> > > > > }
> > > > > catch(A a) // "Warning: Catch clause type is by value for
> polymorphic
> > > > type"
> > > > > {
> > > > >
> > > > > }
> > > > >
> > > > > It'd be sweet (and would get DMC++ a special mention in Part 5,
> which
> > I
> > > > may
> > > > > do next).
> > > > >
> > > > > Matthew
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
> >
>
>

Matthew Wilson schrieb...
> 
> Plain Old Data. Stuff with ctors/dtors/copy-assignment ops/etc.
                        ^^^^
                      without

POD structs should only consist of simple data members. No member
functions at all.
POD type variables can be safely copied with memcopy.

- Heinz

Yes, it was a mistake.

And yes, I agree with all that you've said about POD

"Heinz Saathoff" <hsaat@bre.ipnet.de> wrote in message news:MPG.19afdfd9e86c795f9896ce@news.digitalmars.com...
> Matthew Wilson schrieb...
> >
> > Plain Old Data. Stuff with ctors/dtors/copy-assignment ops/etc.
>                         ^^^^
>                       without
>
> POD structs should only consist of simple data members. No member
> functions at all.
> POD type variables can be safely copied with memcopy.
>
> - Heinz

Hmm. I would think that a POD type would be defined by not having a vptr.

"Heinz Saathoff" <hsaat@bre.ipnet.de> wrote in message news:MPG.19afdfd9e86c795f9896ce@news.digitalmars.com...
> Matthew Wilson schrieb...
> >
> > Plain Old Data. Stuff with ctors/dtors/copy-assignment ops/etc.
>                         ^^^^
>                       without
>
> POD structs should only consist of simple data members. No member
> functions at all.
> POD type variables can be safely copied with memcopy.
>
> - Heinz

Walter schrieb...
> 
> Hmm. I would think that a POD type would be defined by not having a vptr.

Not only that struct but also included structs. The standard says that PODs are classic C-structs which makes sense. This also gives compiler writes more freedom in implementing things. For DMC I know that adding members isn't a problem and I still can memcpy such structs. But it's not guaranteed by the standard.

- Heinz