int main(int argc, char *argv[]) {
@autoreleasepool {
const int x = 1;
const NSMutableArray *array1 = [NSMutableArray array];
const NSMutableString *str1 = @"1";
NSString * const str2 = @"2";
// x = 2; compile error
[array1 addObject:@"2"]; // ok
// [str1 appendString:@"2"]; // runtime error
// Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Attempt to mutate immutable object with appendString:'
// str2 = @"3"; compile error
}
}
我的問題是爲什麼array1 addObject是合法的,爲什麼str1 appendString是禁止的?const關鍵字在objective-c
看到這樣的打擊:
NSMutableString *f2(const NSMutableString * const x) {
[x appendString: @" world!"];
return x;
}
int main(int argc, char *argv[]) {
@autoreleasepool {
NSMutableString *x = [@"Hello" mutableCopy];
NSLog(@"%@", f2(x));
}
return 0;
}
,爲什麼這個代碼是合法的,我怎麼可以讓一個不可變對象使用C「常量」關鍵字就像++?
============================================ @看到https://softwareengineering.stackexchange.com/questions/151463/do-people-use-const-a-lot-when-programming-in-objective-c