Objective-C 中的扩展问题

Question

以下是处理 class 扩展的代码片段。我想做的是生成一个随机 ID，称为内部 ID（稍后由程序使用），它以加密形式存储在内存中。该代码无法用 gcc 和 clang 编译（我是运行 Objective C 通过 GNUStep on Windows），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扩展的使用并在主@interface（即#import 语句之后的接口）本身中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 class 被其他一些子 class 继承，其中 "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;
}

我使用的 gcc 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

我的 clang 的 GNUmakefile 如下：

#
# Command script for clang 
# C:\GNUstep\msys.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

尝试使用 class 扩展中声明的 @property 而不是 ivar 来实现：

#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 private 变量的标准语义，可能更有可能获得编译器支持。

Objective-C 中的扩展问题

Issue with extensions in Objective-C

gcc

objective-c

gnustep

llvm-clang

class-extensions