Objective-C & Private functions
-
Hello -
Is there any way to create private "Helper" functions in
objective-C? I have not been able to find any information on function
scoping within a .h file. Obviously, a function can be declared &
implemented in the .m file, making it somewhat private. However, the
functions pretty much need to be implemented at the top of the .m file
so that other functions can see them. Is there a way to declare
private functions in the .h file, or at the very least, forward declare
them at the top of a .m file, and provide implementation further down
in the .m. Thanks for any help in advance.
--Pete
---------------------------------------------------
Peter S. Fischer
http://macosx.syr.edu/spottedsoftware
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On 8/2/04 6:59 pm, Peter Fischer <pfischer...> wrote:
> Hello -
> Is there any way to create private "Helper" functions in
> objective-C? I have not been able to find any information on function
> scoping within a .h file. Obviously, a function can be declared &
> implemented in the .m file, making it somewhat private. However, the
> functions pretty much need to be implemented at the top of the .m file
> so that other functions can see them. Is there a way to declare
> private functions in the .h file, or at the very least, forward declare
> them at the top of a .m file, and provide implementation further down
> in the .m. Thanks for any help in advance.
Just declare them as static. Static functions follow the same scoping rules
in Objective-C as in ANSI/ISO C.
Cheers,
Chris
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On 2004/02/08, at 13:59, Peter Fischer wrote:
> Hello -
> Is there any way to create private "Helper" functions in
> objective-C? I have not been able to find any information on function
> scoping within a .h file. Obviously, a function can be declared &
> implemented in the .m file, making it somewhat private. However, the
> functions pretty much need to be implemented at the top of the .m file
> so that other functions can see them. Is there a way to declare
> private functions in the .h file, or at the very least, forward
> declare them at the top of a .m file, and provide implementation
> further down in the .m. Thanks for any help in advance.
You can forward declare the functions in the .m file exactly as you
would in the .h file, there is no difference in syntax. Also, if the
function is only to be called from that specific file, it's a good idea
to declare it static, like so:
static void foo(blah);
--
Clark S. Cox III
<clarkcox3...>
http://homepage.mac.com/clarkcox3/
http://homepage.mac.com/clarkcox3/blog/B1196589870/index.html
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@interface SomeClass : NSObject (Private)
-(void)coolFunction1;
-(void)coolFunction2;
@end
Forgive any syntax misses here since I'm at work and cannot verify what
I'm typing. But it should give you the idea.
> Hello -_______________________________________________
> Is there any way to create private "Helper" functions in
> objective-C? I have not been able to find any information on function
> scoping within a .h file. Obviously, a function can be declared &
> implemented in the .m file, making it somewhat private. However, the
> functions pretty much need to be implemented at the top of the .m file
> so that other functions can see them. Is there a way to declare
> private functions in the .h file, or at the very least, forward declare
> them at the top of a .m file, and provide implementation further down
> in the .m. Thanks for any help in advance.
>
> --Pete
>
> ---------------------------------------------------
> Peter S. Fischer
> http://macosx.syr.edu/spottedsoftware
> _______________________________________________
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On Feb 8, 2004, at 1:59 PM, Peter Fischer wrote:
> Is there any way to create private "Helper" functions in
> objective-C? I have not been able to find any information on function
> scoping within a .h file. Obviously, a function can be declared &
> implemented in the .m file, making it somewhat private. However, the
> functions pretty much need to be implemented at the top of the .m file
> so that other functions can see them. Is there a way to declare
> private functions in the .h file, or at the very least, forward
> declare them at the top of a .m file, and provide implementation
> further down in the .m. Thanks for any help in advance.
Objective-C doesn't have the ability to declare methods as public,
private, or protected - they're all public. You can declare variables
as protected, public or private, although I honestly haven't really
seen that done much. Cocoa is a much more trusting language than Java
and C++, which are rather paranoid languages. =)
There are a couple of ways of doing the equivalent. One of them is what
you've mentioned - simply not including the method in your header file.
Another way that Apple's engineers seem to use a lot is to declare
categories specifically for blocks of related "private" functionality.
The category can be contained in a separate header and, thus, the
methods won't be obvious to outside coders. If someone does a little
reverse engineering and discovers your method, there's nothing
preventing them from calling it, but any decent Cocoa developer is
going to know that they are using a "private" undocumented method at
their own risk.
Basically, Obj-C will let you call any method (actually "send any
message" is technically what you're doing) on any object without error
(though it won't do anything if the method doesn't exist) - this
ability is inherent in the basic underlying design of Cocoa. By
declaring your methods in a category, or by not including them in your
header file, you are saying "Beware, proceed at your own risk." Don't
worry about totally locking people out the way you do in Java. After
spending some time in Obj-C, you'll come to realize that there's far
less need to do that than you once thought (I know... I asked this
exact same question about 3 years ago on this list). Objective-C's
syntax can be learned in a day, but it takes a little longer to really
wrap your head around it.
Jeff
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On Feb 8, 2004, at 1:59 PM, Peter Fischer wrote:
> Is there any way to create private "Helper" functions in
> objective-C? I have not been able to find any information on function
> scoping within a .h file. Obviously, a function can be declared &
> implemented in the .m file, making it somewhat private.
To create a "private" function that's local to the current compilation
unit, use "static" as in:
static int min(int a, int b) {
return (a < b) ? a : b;
}
If you mean methods rather than functions, then there is generally no
such thing as access control on methods in a true object-oriented
language like Objective-C or Smalltalk. A method is called in response
to a message, and you can send any message to any object at any time.
> However, the functions pretty much need to be implemented at the top
> of the .m file so that other functions can see them. Is there a way
> to declare private functions in the .h file, or at the very least,
> forward declare them at the top of a .m file, and provide
> implementation further down in the .m. Thanks for any help in
> advance.
One workaround is to declare methods you don't want to expose in a
category:
@interface MyClass (BDInternalMethods)
- (void)privateMethodOne;
@end
atop your implementation (.m) file or in a separate header file, and
then define them in a category too:
@implementation MyClass (BDInternalMethods)
- (void)privateMethodOne {
NSLog(@"-[MyClass(BDInternalMethods) privateMethodOne]");
}
@end
Note that the user can run class-dump on a binary and see both the
category and the methods within it, and someone could write code that
sends your object -privateMethodOne as well. But if they don't have or
include your separate header, they may get a compiler warning that
MyClass doesn't respond to -privateMethodOne.
-- Chris
--
Chris Hanson <cmh...>
bDistributed.com, Inc.
Outsourcing Vendor Evaluation
Custom Mac OS X Development
Cocoa Developer Training
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On Feb 8, 2004, at 1:59 PM, Peter Fischer wrote:
> Hello -
> Is there any way to create private "Helper" functions in
> objective-C? I have not been able to find any information on function
> scoping within a .h file. Obviously, a function can be declared &
> implemented in the .m file, making it somewhat private. However, the
> functions pretty much need to be implemented at the top of the .m file
> so that other functions can see them. Is there a way to declare
> private functions in the .h file, or at the very least, forward
> declare them at the top of a .m file, and provide implementation
> further down in the .m. Thanks for any help in advance.
>
> --Pete
Assuming you want an Objective C method that's private, and not a C
function, the way people usually do this is to use a Category:
In file Foo.m:
@interface Foo (PrivateMethods)
- (void) doSomethingPrivate;
@end
@implementation Foo
- (void) somethingPublic {
[self doSomethingPrivate];
//... etc
}
You can use categories for a bunch of stuff
* amazingly enough, Categorizing your methods, which makes them easier
to find in the IDE
* adding methods to other classes, even those you don't have the source
to
* simulating things like private methods
They're something you don't see in Java and other similar languages so
they're definitely worth taking a few moments to understand.
AndyT (lordpixel - the cat who walks through walls)
A little bigger on the inside
(see you later space cowboy ...)
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