Thu, 01 Dec 2005

Return of Accessors vs. public member variables

Steinar, Imagine a Word class: 

class WordA {
   public:
      char * word;
};
class WordB {
   private:
      char * word;
   public:
      void setWord(char * w) { word = w; }
      char * getWord() { return word; }
};

WordA worda; 
worda.word = "WordA";

WordB wordb;
wordb.setWord("WordB");

printf("%s %s", worda.word, wordb.getWord());

Fine, this works well. Now imagine that you want to change word from a char * to a std::string to stop you dealing with pointers. For the WordBclass you only need to change the getWord function. You don't need to change any of your class's users. For the WordA class, you have a problem because you can't automatically convert from a std::string to a char *, so all your users have to change from object.word to object.word.c_str(). 

class WordA {
   public:
      std::string word;
};
class WordB {
   private:
      std::string word;
   public:
      void setWord(char * w) { word = w; }
      char * getWord() { return word.c_str(); }
};

WordA worda; 
worda.word = "WordA";

WordB wordb;
wordb.setWord("WordB");

printf("%s %s", worda.word.c_str(), wordb.getWord());

This is the punishment you get for exposing the internal details of your class to your users. Please ignore any specific mistakes in my examples; the principles work the same with different types.

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