Minor problem messaging C++ wrappers in Objective-C with gcc4.2
Hi,
I've found it very useful to be able to use C++ to extend Objective-C
using a little judicious operator overloading and I notice that gcc-4.2
now automatically "unboxes" wrapper classes with no warning when
they are messaged - provided an appropriate cast is available.
For example:
class AStringClass {
NSMutaableString *str;
public:
AStringClass( NSMutableString *str ) {
this->str = str;
}
operator NSMutableString * () {
return str;
}
};
This class can now be messaged in gcc4.2 as below without a warning:
AStringClass aString( nil );
[aString doubleValue];
Unfortunately is can also be sent a message which the compiler
is in a position to know is not available given the only cast
available was to a NSMutableString:
[aString count]; // not a valid method for NSMutableString *
This happens as internally as there is an implicit cast to type "id" in
${GCCROOT}gcc/objc/objc-act,c, function: objc_finish_message_expr
/* APPLE LOCAL begin decay function/array receivers */
#ifndef OBJCPLUS
/* In C need to decay array/function receivers so can be converted
to id. */
struct c_expr exp;
exp.value = receiver;
exp = default_function_array_conversion (exp);
receiver = exp.value;
/* APPLE LOCAL begin radar 3533972 */
#else
if (can_convert_arg (objc_object_type, TREE_TYPE (receiver),
receiver, LOOKUP_NORMAL))
{
/* In rare cases, 'receiver' must be converted to type 'id' using
user-defined type conversion. 'id' is type of the 1st
argument to
objc_msgSend (id self, SEL op, ...); */
tree cnv_rec = perform_implicit_conversion (objc_object_type,
receiver);
if (cnv_rec && cnv_rec != error_mark_node)
return objc_finish_message_expr (cnv_rec, sel_name,
method_params);
}
/* APPLE LOCAL end radar 3533972 */
#endif
Would it not be possible for the implicit conversion retain the type
which it was forced into using when searching for a match for "id"
and using this as the type of the receiver of the message rather
than "id". I've looked and the code but can't quite get to where
the change (probably quite a small one) would need to be made.
Perhaps even, this is already fixed...
Can anybody help?
John Holdsworth
objcpp.johnholdsworth.com
On 8 Apr 2009, at 14:34, David Ayers wrote:
Am Samstag, den 21.03.2009, 11:59 +0100 schrieb John Holdsworth:
I was wondering if it would be a useful extension to Objective-C
expand the [] operator
to support array and hash references to NSArray and NSDictionary
classes directly to
greatly improve the readability of code:
I'm not an ObjC front end maintainer and have no authority but one
issue
I would have with this feature with gcc proper is that the ObjC front
end would have to learn about the semantics of "NSArray" and
"NSDictionary" which are actually not part of the language but part of
an external library.
Now gcc already supports the -fconstant-string-class option as one way
to embed knowledge about an external library into an executable.
But I
would like adding options with all these semantics from a foreign
library into the language implementation.
Maybe this could be done more elegantly with plugin infrastructure
that
that es being currently added: http://gcc.gnu.org/wiki/plugins
Cheers,
David
Bus error gcc compiler for any for ( x in array ) inside Objective-C++ template
Hi,
I've encountered a bus error using Apple's gcc in Xcode 3.1, 3.2
compiling the following code or any containing for( x in y ) is used
inside a template in Objective-C++.
template
class OODictionary {
void boom() {
NSArray *keys = nil;
for ( NSString *key in keys ) {
}
}
};
I've not been able to build with a more recent gcc so I can't tell
if it is still present but figure I'd better let you guys know.
Thanks,
John H.
http://objcpp.johnholdsworth.com
On 8 Sep 2009, at 21:30, John Holdsworth wrote:
Hi,
I've found it very useful to be able to use C++ to extend Objective-C
using a little judicious operator overloading and I notice that
gcc-4.2
now automatically "unboxes" wrapper classes with no warning when
they are messaged - provided an appropriate cast is available.
For example:
class AStringClass {
NSMutaableString *str;
public:
AStringClass( NSMutableString *str ) {
this->str = str;
}
operator NSMutableString * () {
return str;
}
};
This class can now be messaged in gcc4.2 as below without a warning:
AStringClass aString( nil );
[aString doubleValue];
Unfortunately is can also be sent a message which the compiler
is in a position to know is not available given the only cast
available was to a NSMutableString:
[aString count]; // not a valid method for NSMutableString *
This happens as internally as there is an implicit cast to type "id"
in
${GCCROOT}gcc/objc/objc-act,c, function: objc_finish_message_expr
/* APPLE LOCAL begin decay function/array receivers */
#ifndef OBJCPLUS
/* In C need to decay array/function receivers so can be converted
to id. */
struct c_expr exp;
exp.value = receiver;
exp = default_function_array_conversion (exp);
receiver = exp.value;
/* APPLE LOCAL begin radar 3533972 */
#else
if (can_convert_arg (objc_object_type, TREE_TYPE (receiver),
receiver, LOOKUP_NORMAL))
{
/* In rare cases, 'receiver' must be converted to type 'id'
using
user-defined type conversion. 'id' is type of the 1st
argument to
objc_msgSend (id self, SEL op, ...); */
tree cnv_rec = perform_implicit_conversion (objc_object_type,
receiver);
if (cnv_rec && cnv_rec != error_mark_node)
return objc_finish_message_expr (cnv_rec, sel_name,
method_params);
}
/* APPLE LOCAL end radar 3533972 */
#endif
Would it not be possible for the implicit conversion retain the type
which it was forced into using when searching for a match for "id"
and using this as the type of the receiver of the message rather
than "id". I've looked and the code but can't quite get to where
the change (probably quite a small one) would need to be made.
Perhaps even, this is already fixed...
Can anybody help?
John Holdsworth
objcpp.johnholdsworth.com
On 8 Apr 2009, at 14:34, David Ayers wrote:
Am Samstag, den 21.03.2009, 11:59 +0100 schrieb John Holdsworth:
I was wondering if it would be a useful extension to Objective-C
expand the [] operator
to support array and hash references to NSArray and NSDictionary
classes directly to
greatly improve the readability of code:
I'm not an ObjC front end maintainer and have no authority but one
issue
I would have with this feature with gcc proper is that the ObjC front
end would have to learn about the semantics of "NSArray" and
"NSDictionary" which are actually not part of the language but part
of
an external library.
Now gcc already supports the -fconstant-string-class option as one
way
to embed knowledge about an external library into an executable.
But I
would like adding options with all these semantics from a foreign
library into the language implementation.
Maybe this could be done more elegantly with plugin infrastructure
that
that es being currently added: http://gcc.gnu.org/wiki/plugins
Cheers,
David
Re: Syntactic sugar to access arrays and hashes in Objective-C
Hi gcc'ers,
I was wondering if it would be a useful extension to Objective-C
expand the [] operator
to support array and hash references to NSArray and NSDictionary
classes directly to
greatly improve the readability of code:
NSArray *players = [NSArray arrayWithObjects:..., nil];
[players[0] play]; // expanded by compiler to: [(AVAudioPlayer *)
[players objectAtIndex:0] play];
players[0] = aPlayer // expanded to: [players replaceObjectAtIndex:0
withObject:aPlayer]; or for NSDictionary:
NSDictionary *playersDict = [NSDictionary ];
[playersDict[@"playerOne"] play]; // -> [(AVAudioPlayer *)[playersDict
objectForKey:@"playerOne"] play];
playersDict[@"playerTwo"] = aPlayer; // becomes: [players
setObject:aPlayer forKey:@"playerTwo"];
This also makes use of a form of templates for Objective-C containers
which might also be a useful extension.
@interfcae NSArray : NSObject {
- (T)objectAtIndex:(NSUInteger)index;
@end
@interface NSMutableObject : NSArray {
- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(T)anObject
@end
Where not specified, type T would default to (id) for backward
compatibility.
I've looked at the code and such an extension would involve code
generation inside
the subscript operator which looks difficult but if you want me to
have a go and
can provide some pointers let me know. I know this introduces coupling
between
the compiler and the runtime but I would have thought the benefits
outweighed this.
Perhaps classes which wish to support subscripting make methods
available by convention:
for NSArray:
- (id)operatorSubscriptInt:(NSUInteger)index;
- (id)operatorSubscriptObject:(id)key;
for NSDictionary
- (id)operatorSubscriptInt:(NSUInteger)index setValue:(id)anObject;
- (id)operatorSubscriptObject:(id)key setValue:(id)anObject;
I know, it sounds like one step on the way to operator overloading
Best Regards & Thanks for your work,
John Holdsworth
Re: Syntactic sugar to access arrays and hashes in Objective-C
Hi David, Thanks for the reply, I've managed to find a solution for my needs in the end. It turns out the Apple gcc compiler supports mixing C++ and Objective-C in the same source file so I've been able to implement what I was looking for using operator overloading - a much more flexible solution that doesn't require the compiler to have knowledge of Apple's XCode core libraries. I've attached the source, its a rather odd hybrid to say the least: The documentation is here: http://johnholdsworth.com/objcpp/html I need to write the unit tests now.. I'm not sure its saved me any time in reality but it was an interesting digression and hopefully it will be useful to somebody :) objcpp.h Description: Binary data Cheers, John Holdsworth On 8 Apr 2009, at 14:34, David Ayers wrote: Am Samstag, den 21.03.2009, 11:59 +0100 schrieb John Holdsworth: I was wondering if it would be a useful extension to Objective-C expand the [] operator to support array and hash references to NSArray and NSDictionary classes directly to greatly improve the readability of code: I'm not an ObjC front end maintainer and have no authority but one issue I would have with this feature with gcc proper is that the ObjC front end would have to learn about the semantics of "NSArray" and "NSDictionary" which are actually not part of the language but part of an external library. Now gcc already supports the -fconstant-string-class option as one way to embed knowledge about an external library into an executable. But I would like adding options with all these semantics from a foreign library into the language implementation. Maybe this could be done more elegantly with plugin infrastructure that that es being currently added: http://gcc.gnu.org/wiki/plugins Cheers, David
