Re: "weak link" framework refs for 10.1 compatibility?

FROM : Marco Scheurer
DATE : Mon Nov 11 17:27:48 2002

On Monday, November 11, 2002, at 02:52 PM, Ondra Cada wrote:

> On Monday, November 11, 2002, at 12:23 , Bill Cheeseman wrote:
>
>>> Wow -- you sure? With the method it is just natural, but with
>>> constants it
>>> should not work, so far as I understand how the linker behaves :-O
>>> :-O
>>
>> These are enumeration constants in a typedef.
>
> Ah. I havent checked -- I live in 10.1, so to speak ;), and had no
> 10.2 at hand at the moment.

Well, the constant declaration I was refering to was in full in my
first email:

#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_2
typedef enum {
    NSTextFieldSquareBezel  = 0,
    NSTextFieldRoundedBezel = 1
} NSTextFieldBezelStyle;
#endif

> Also, I did never suppose that such an experienced programmer as Marco
> is would use such a self-evidently nonsensical example as using a
> constant from a header... Sigh.

Yeah, I did not understand the "C constant" part, reason why I was
surprised by a statement such as "an application using C constants that
are new in 10.2 will not launch in 10.1.x or earlier".

The fact that they are constant has nothing to do with the problem, the
problem is that they are externally linked C variables, or storage. Or,
said differently, in:

FOUNDATION_EXPORT NSString *const NSFileImmutable;

the runtime problem on 10.1 is not with "const", the error will be the
same with or without it.

In the "enum" case the compiler will replace the constant with its
value, and if building on 10.1 we would get a compile-time error.

In the "variable" case, if building the following on 10.1, we would get
an error at link time.

> -(void) testing { // TESTING
>    NSString *string = NSFileImmutable;
>    NSLog(@"NSFileImmutable = %@", string);
> }

Marco Scheurer
Sen:te, Lausanne, Switzerland    http://www.sente.ch
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