Objective-C中的扩展问题

Question

以下是处理类扩展的代码段.我要做的是生成一个称为内部ID的随机ID(稍后由程序使用),它以加密形式存储在内存中.代码无法使用gcc和clang编译(我在Windows上通过GNUStep运行Objective C),每个编译器都有不同的错误消息,在代码中作为注释提到.

请注意,我知道这个问题可以通过忽略主@faceface(即#import语句之后的那个)本身的扩展和声明方法和属性来轻松解决.我使用扩展的唯一原因是这个类是由一些其他子类继承的,"internalID"属性必须是不可访问的.

#import <Foundation/Foundation.h>

@interface Foo : NSObject
{
    NSString * idStr;
}
- (void)setInternalID;
- (NSString *)fetchExternalID;
@end

// Extension declaration
@interface Foo()
{ // Compilation via gcc throws error at this line stating "Expected identifier or '(' before '{' token"
    NSString *internalID; // Compilation via clang throws error at this line stating "instance variables may not be placed in class extension"
}
@end

@implementation Foo
- (void)setInternalID{
    internalID = [NSString stringWithFormat: 
    @"__KEY__INTERNAL__DUMP2872167841398551___8765%d98KLPYFGF(&^$#ESFK___JNHGV",arc4random()%100];
}
- (NSString *)fetchExternalID{
    NSString * externalID=[internalID stringByReplacingOccurrencesOfString: 
    @"__KEY__INTERNAL__DUMP2872167841398551___8765" withString:@""];
    externalID=[externalID stringByReplacingOccurrencesOfString: 
    @"98KLPYFGF(&^$#ESFK___JNHGV" withString:@""];
    return externalID;
}
@end

int main(int argc, const char * argv[])
{
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    Foo * bar = [[Foo alloc]init];
    [bar setInternalID];
    NSLog(@"External ID: %@",[bar fetchExternalID]);        
    [pool drain];
    return 0;
}

我正在使用的gcc的编译字符串是 gcc -o _exec fwdORM.m -I /GNUstep/System/Library/Headers -L /GNUstep/System/Library/Libraries -lobjc -lgnustep-base -fconstant-string-class=NSConstantString

我对clang的GNUmakefile如下:

#
# Command script for clang 
# C:\GNUstep\msys\1.0\home\hecate\my\GNUmakefile
#

GNUSTEP_MAKEFILES=/GNUStep/System/Library/Makefiles

include $(GNUSTEP_MAKEFILES)/common.make

TOOL_NAME = fwdORM

fwdORM_OBJC_FILES = fwdORM.m
fwdORM_OBJCFLAGS = -std=c99

# Implementation mixing Objective-C/CPP file going to be compiled; Currently not required
#fwdORM_OBJCC_FILES = fwdORM_21.mm

# Implementation CPP file going to be compiled; Currently N/A
#fwdORM_CC_FILES = sec_class_exec.cpp

# Header files of project
#fwdORM_HEADER_FILES = .h // N/A

# Define compilation flags
ADDITIONAL_CPPFLAGS = -Wall -Wno-import -fblocks

# Include rules for creating a command line tool for Objective-C
include $(GNUSTEP_MAKEFILES)/tool.make

提前致谢.

Answer 1

尝试通过使用@property类扩展中声明的而不是 ivar 来实现此目的：

#import <Foundation/Foundation.h>

@interface Foo : NSObject
- (void)setInternalID;
- (NSString *)fetchExternalID;
@end

// Extension declaration
@interface Foo()
@property (strong) NSString *internalID;
@end

@implementation Foo

- (void)setInternalID {
    self.internalID = [NSString stringWithFormat:@"__KEY__INTERNAL__DUMP2872167841398551___8765%d98KLPYFGF(&^$#ESFK___JNHGV",arc4random()%100];
}

- (NSString *)fetchExternalID {
    NSString * externalID = [self.internalID stringByReplacingOccurrencesOfString:@"__KEY__INTERNAL__DUMP2872167841398551___8765" withString:@""];
    externalID = [externalID stringByReplacingOccurrencesOfString:@"98KLPYFGF(&^$#ESFK___JNHGV" withString:@""];
    return externalID;
}

@end

这是有效变量的标准语义private，并且可能更有机会获得编译器支持。