Object-C 牛刀小試 (存取權限)

權限問題

• 預設的權限是 @protected
• Java 實作的方式是在 methods 與變數前面加上 public/private/protected 修飾語，而 Objective-C 的作法則更像 C++ 對於 instance variable（C++ 術語 data members）的方式。
• Access.h

  #import <Foundation/NSObject.h>
  
  @interface Access: NSObject {
  @public
      int publicVar;
  @private
      int privateVar;
      int privateVar2;
  @protected
      int protectedVar;
  }
  @end

• Access.m

  #import "Access.h"
  
  @implementation Access
  @end

• main.m

  #import "Access.h"
  #import <stdio.h>
  
  int main( int argc, const char *argv[] ) {
      Access *a = [[Access alloc] init];
  
      // works
      a->publicVar = 10;
      printf( "public var: %i\n", a->publicVar );
  
      // doesn't compile
      //a->privateVar = 100;
      //printf( "private var: %i\n", a->privateVar );
  
      [a release];
      return 0;
  }

• output

  public var: 10

• C++ 中 private: [list of vars] public: [list of vars] 的格式，它只是改成了@private, @protected, 等等。