Re: Coding style

[Hans Aberg]

On 13 Jan 2011, at 16:50, David Kastrup wrote:
> Doesn't C++ have some more useful
> idiom for iterators or so?

Then you'd have to write a function to apply. Below is an example; I  
let you decide if it is more useful. :-)

> Something like
>
>    for (d=UP;;d=DOWN) {
>      ...
>      if (d == DOWN)
>         break;
>    }
>
> would be somewhat prettier in my book and involve less calculation.


Or
  for (d=UP;d==UP;d=DOWN) {
    ...
  }
or
  #define UPDOWN(x) for ((d)=UP;(d)==UP;(d)=DOWN)
  UPDOWN(d) {
    ...
  }

But macros and templates tend to produce nasty errors.


---- up_down.cc ----

#include <iostream>
#include <algorithm>

struct up_down {
  enum token { UP, DOWN, END } _value;

  up_down() : _value(UP) {}
  up_down(token x) : _value(x) {}

  token operator*() { return  _value; }
  token operator++() {
    switch (_value) {
      case UP: _value = DOWN; break;
      default: _value = END;
    };
    return _value;
  }

  friend bool operator==(const up_down& x, const up_down& y) { return  
x._value == y._value; }
  friend bool operator!=(const up_down& x, const up_down& y) { return  
x._value != y._value; }

  static up_down begin() { return UP; }
  static up_down end() { return END; }
};


void f(up_down::token x) {
  switch (x) {
    case up_down::UP: std::cout << "Hello "; return;
    case up_down::DOWN: std::cout << "World!"; return;
  };
}

int main() {
  std::for_each(up_down::begin(), up_down::end(), f);
  std::cout << std::endl;
  return EXIT_SUCCESS;
}
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