instanceof in CNI

instanceof in CNI

[Oskar Liljeblad]

Hello

Is there anything similar to the Java instanceof operatior in C++/CNI?

Oskar Liljeblad (osk@hem.passagen.se)

Re: instanceof in CNI

[Bryce McKinlay]

Oskar Liljeblad wrote:

> Is there anything similar to the Java instanceof operatior in C++/CNI?

You can use _Jv_IsInstanceOf(object, class)

To get a reference to a Class object to compare against, you currently
have to use Class::forName(), or compare against the mangled symbolic
class name directly. This is something we're looking at addressing soon
in gcjh.

regards

  [ bryce ]

Re: instanceof in CNI

[Tom Tromey]

>> Is there anything similar to the Java instanceof operatior in C++/CNI?

Bryce> You can use _Jv_IsInstanceOf(object, class)

Usually we recommend only using "Jv" functions and not "_Jv_"
functions.  The former are exported and the latter are not.

I recommend using Class::isInstance.

Bryce> To get a reference to a Class object to compare against, you
Bryce> currently have to use Class::forName(), or compare against the
Bryce> mangled symbolic class name directly. This is something we're
Bryce> looking at addressing soon in gcjh.

Lately I've been thinking gcjh could generate a per-class inline
function named something like "$class"; I got this idea because
apparently javac generates an internal function named "class$" to
implement the ".class" notation.

Comments?  Naming here is the big problem, as I see it.

Tom

Re: instanceof in CNI

[Per Bothner]

Tom Tromey <tromey@cygnus.com> writes:

> Lately I've been thinking gcjh could generate a per-class inline
> function named something like "$class"; I got this idea because
> apparently javac generates an internal function named "class$" to
> implement the ".class" notation.

The compiler generates a static field the the actuall
Class object.  If we picked a good name for this,
we could have gcjg also emit it.

E.g.
class java::lang::String : public java::lang::Object
{
  java::lang::Class $class;
}

Then you'd just reference String::$class .
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/~per/

Re: instanceof in CNI

[Tom Tromey]

Per> class java::lang::String : public java::lang::Object
Per> {
Per>   java::lang::Class $class;
Per> }
Per> Then you'd just reference String::$class .

Do you mean `Class *$class'?  To me that seems more natural.  We could
do that without changing the mangling or anything; just add a new
static to each class.

Tom

Re: instanceof in CNI

[Per Bothner]

Tom Tromey <tromey@cygnus.com> writes:
> Do you mean `Class *$class'?  To me that seems more natural.  We could
> do that without changing the mangling or anything; just add a new
> static to each class.

No, I mean Class $class.  The thing is - we already generate a
static Class field (not Class* field) - the actual Class object.
We just need to make sure it has a reasonable name (`class'
would be nice, since that's what Java does in the syntax `String.class'.
Unfortunately, the C++ parser won't like that, without ugly hacking
that seems hard to justify.  Hence `$class'.

There are other options, including the inline function you
suggested, or a builtin operator like __jv_classof.  I like
the simplicit of using thefield we are already generating.
I think we are currently calling it `class'.

	--Per Bothner
per@bothner.com   http://www.bothner.com/~per/

Re: instanceof in CNI

[ks]

The standard C++ mechanism is to use RTTI as in:

   typeof<foo> == typeof<bar>

but I think that C++ RTTI interferes with Java if I remember correctly.

On Sat, Mar 25, 2000 at 12:52:54PM +0100, osk@hem.passagen.se wrote:
> Hello
> 
> Is there anything similar to the Java instanceof operatior in C++/CNI?
> 
> Oskar Liljeblad (osk@hem.passagen.se)

Re: instanceof in CNI

[Tom Tromey]

>>>>> "ks" == ks  <ks@micky.rgv.hp.com> writes:

ks> The standard C++ mechanism is to use RTTI as in:
ks>    typeof<foo> == typeof<bar>
ks> but I think that C++ RTTI interferes with Java if I remember correctly.

That's right, they don't interoperate.
This would probably be a good thing to do.
However, it is a very low priority for us; odds are it will have to
wait for a net volunteer to write it.

Tom

instanceof in CNI

[Oskar Liljeblad]

Hello

Is there anything similar to the Java instanceof operatior in C++/CNI?

Oskar Liljeblad (osk@hem.passagen.se)

Re: instanceof in CNI

[Tom Tromey]

>>>>> "ks" == ks  <ks@micky.rgv.hp.com> writes:

ks> The standard C++ mechanism is to use RTTI as in:
ks>    typeof<foo> == typeof<bar>
ks> but I think that C++ RTTI interferes with Java if I remember correctly.

That's right, they don't interoperate.
This would probably be a good thing to do.
However, it is a very low priority for us; odds are it will have to
wait for a net volunteer to write it.

Tom

Re: instanceof in CNI

[Tom Tromey]

Per> class java::lang::String : public java::lang::Object
Per> {
Per>   java::lang::Class $class;
Per> }
Per> Then you'd just reference String::$class .

Do you mean `Class *$class'?  To me that seems more natural.  We could
do that without changing the mangling or anything; just add a new
static to each class.

Tom

Re: instanceof in CNI

[ks]

The standard C++ mechanism is to use RTTI as in:

   typeof<foo> == typeof<bar>

but I think that C++ RTTI interferes with Java if I remember correctly.

On Sat, Mar 25, 2000 at 12:52:54PM +0100, osk@hem.passagen.se wrote:
> Hello
> 
> Is there anything similar to the Java instanceof operatior in C++/CNI?
> 
> Oskar Liljeblad (osk@hem.passagen.se)

Re: instanceof in CNI

[Per Bothner]

Tom Tromey <tromey@cygnus.com> writes:

> Lately I've been thinking gcjh could generate a per-class inline
> function named something like "$class"; I got this idea because
> apparently javac generates an internal function named "class$" to
> implement the ".class" notation.

The compiler generates a static field the the actuall
Class object.  If we picked a good name for this,
we could have gcjg also emit it.

E.g.
class java::lang::String : public java::lang::Object
{
  java::lang::Class $class;
}

Then you'd just reference String::$class .
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/~per/

Re: instanceof in CNI

[Bryce McKinlay]

Oskar Liljeblad wrote:

> Is there anything similar to the Java instanceof operatior in C++/CNI?

You can use _Jv_IsInstanceOf(object, class)

To get a reference to a Class object to compare against, you currently
have to use Class::forName(), or compare against the mangled symbolic
class name directly. This is something we're looking at addressing soon
in gcjh.

regards

  [ bryce ]

Re: instanceof in CNI

[Per Bothner]

Tom Tromey <tromey@cygnus.com> writes:
> Do you mean `Class *$class'?  To me that seems more natural.  We could
> do that without changing the mangling or anything; just add a new
> static to each class.

No, I mean Class $class.  The thing is - we already generate a
static Class field (not Class* field) - the actual Class object.
We just need to make sure it has a reasonable name (`class'
would be nice, since that's what Java does in the syntax `String.class'.
Unfortunately, the C++ parser won't like that, without ugly hacking
that seems hard to justify.  Hence `$class'.

There are other options, including the inline function you
suggested, or a builtin operator like __jv_classof.  I like
the simplicit of using thefield we are already generating.
I think we are currently calling it `class'.

	--Per Bothner
per@bothner.com   http://www.bothner.com/~per/

Re: instanceof in CNI

[Tom Tromey]

>> Is there anything similar to the Java instanceof operatior in C++/CNI?

Bryce> You can use _Jv_IsInstanceOf(object, class)

Usually we recommend only using "Jv" functions and not "_Jv_"
functions.  The former are exported and the latter are not.

I recommend using Class::isInstance.

Bryce> To get a reference to a Class object to compare against, you
Bryce> currently have to use Class::forName(), or compare against the
Bryce> mangled symbolic class name directly. This is something we're
Bryce> looking at addressing soon in gcjh.

Lately I've been thinking gcjh could generate a per-class inline
function named something like "$class"; I got this idea because
apparently javac generates an internal function named "class$" to
implement the ".class" notation.

Comments?  Naming here is the big problem, as I see it.

Tom