The Missing Things in C++

Originally published on 2007-09-18 in the Masthead Developer Blog.

Published in Bulgarian on the defunct SourceCore in 2004.

These are a few of the things that we mused would be, if not practical, then at least interesting to have.

dont - keyword, doesn’t do what’s in its block:

dont {
   cout << "this program is stupid" << endl; //yep, it's not
   remove("win.com"); //definitely don't do this
   crash(); //d'oh
}

Possible implementation with standard C++:

#define dont if(false)

that - keyword, similar to this, a pointer to a random instance of a class:

void someclass::somemethod()
{
   that->m_var = 10; //someone got a ten, good luck...
}

Unfortunately a clean implementation in the current standard is impossible, but can be done intrusively like so:

template <class T>
class _thatable
{
protected:
   _thatable() { m_thats.push_back(this); }
   ~_thatable() { m_thats.erase(find(m_thats.begin(), m_thats.end(), this)); }
   T* _my_that() {
      return m_thats[rand()%m_thats.size()];
   }
private:
   static vector<T*> m_thats;
};

#define cool_class(x) class x : public _thatable<x>
#define that _my_that()

… and used like so:

cool_class(myclass) , public other_parent
{
...
};

#outclude - preprocessor, removes all declarations that were previously brought in with an #include

#outclude <vector>
//...
vector<int> a; // ERROR

Unfortunately, it’s impossible to implement with the current standard.

maybe - keyword, sometimes returns true, sometimes false…

bool hmm = maybe;
if( hmm )
    cout << "Hello, world" ;
else
    dont { cout << "Hello, world"; }

Pretty straightforward to implement:

struct {
   operator bool () const {
      return rand() % 2;
   }
} maybe;

disusing and disusing namespace - removes a symbol or all symbols in a namespace from the current scope.

disusing namespace std;
string str; // huh?..

private_cast and protected_cast - similar to const_cast, allows access to otherwise inaccessible sections of a class.

class x { int b; } a;
private_cast(a).b = 5;

private_cast is impossible to implement in general. protected_cast on the other hand can be implemented in several ways.