Talk:Trait

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(Comment provided by jtulach - via ArticleComments extension)
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--[[User:JaroslavTulach|JaroslavTulach]] 22:25, 5 September 2012 (UTC)
--[[User:JaroslavTulach|JaroslavTulach]] 22:25, 5 September 2012 (UTC)
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== jtulach said ... ==
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 +
<div class='commentBlock'>
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The article is more about STL overhead. I personally don't like and don't use STL. I think following C++ implementation is as fast as implementation in C.
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class ll_item;
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 +
class llist {
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public:
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void add(ll_item& p);
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void remove(ll_item& p);
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llist(void);
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~llist();
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};
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class ll_item {
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friend llist;
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private:
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ll_item* next;
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ll_item* prev;
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};
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class person_item : public ll_item {
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protected:
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int age;
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const char* name;
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public:
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person_item(int age, const char* name);
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};
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class animal_item : public ll_item {
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protected:
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const char* name;
 +
 +
public:
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animal_item(const char* name);
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};
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int main(int argc, char* argv[])
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{
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person_item a(10, "Ben");
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person_item b(20, "Nora");
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person_item c(30, "John");
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animal_item x("Fifi");
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animal_item y("Bobika");
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animal_item z("Bill");
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llist l;
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l.add(b);
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l.add(c);
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l.add(a);
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l.add(x);
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l.add(y);
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l.add(z);
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}
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 +
--jtulach 21:07, 11 September 2012 (CEST)
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</div>

Revision as of 19:07, 11 September 2012

Comments on Trait <comments />

Miles Elam said ...

Yes, this is indeed possible in C++ and is, in fact, used extensively in the C++ standard library (aka STL). For a prime example, look no further than std::string or the various pluggable memory allocators. The example given in the article appears to these eyes as one of a C programmer trying to make C++ do things like C and failing. To be more precise, if one is accessing people objects by iterator, why would a raw pointer to a person need to be manipulated in this way? In addition, what happens if the object must be accessed in multiple ways, e.g., exists in both a normal list and a sorted list (or multiple sorted lists). The C method falls down as there is no single pair of *next and *prev but rather multiple.

Don't get me wrong, C definitely has its uses. Its relative simplicity for one. However, C++'s generic algorithms and data structures should not be discarded so lightly.

--Miles Elam 20:26, 4 September 2012 (CEST)

I am primarily interested in properly typing the multiple class encapsulation case. E.g. having prev/next field in the item class and manipulating them in only by the list. Moreover I'd like to write this (and type this) in a generic way. Looks like it will be possible to do it in C++, but the solution will definitely not be like in Java/Scala - rather upside-down...

--JaroslavTulach 22:25, 5 September 2012 (UTC)

jtulach said ...

The article is more about STL overhead. I personally don't like and don't use STL. I think following C++ implementation is as fast as implementation in C.

class ll_item;

class llist { 

 public:
   void add(ll_item& p);
   void remove(ll_item& p);

   llist(void);
  ~llist();

};

class ll_item { 

   friend llist;
 private:
   ll_item* next;
   ll_item* prev;

};


class person_item : public ll_item { 

 protected:
   int age;
   const char* name;

 public:
   person_item(int age, const char* name);

};

class animal_item : public ll_item { 

 protected:
   const char* name;

 public:
   animal_item(const char* name);

};

int main(int argc, char* argv[]) { 

 person_item a(10, "Ben");
 person_item b(20, "Nora");
 person_item c(30, "John");

 animal_item x("Fifi");
 animal_item y("Bobika");
 animal_item z("Bill");

 llist l;
 l.add(b);
 l.add(c);
 l.add(a);
 l.add(x);
 l.add(y);
 l.add(z);

}

--jtulach 21:07, 11 September 2012 (CEST)

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