Re: Suggested extention of the break statement

From:
kevin cline <kevin.cline@gmail.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Sat, 8 Sep 2007 03:48:04 CST
Message-ID:
<1189236392.032919.215090@w3g2000hsg.googlegroups.com>
On Aug 23, 6:11 pm, Hyman Rosen <hyro...@mail.com> wrote:

The current single-level break and continue statements are
inadequate for many reasonable loop structures anyway. C++
should take a page from Ada and allow 'break label;' and
'continue label;' where label is attached to a statement.
(We would require that the label for a continue actually
label a loop, but any statement could have a break label.)
So,

     t1: try {
         stuff();
         if (condition()) {
             break t1;
         }
     } catch (...) {
         handle();
     }


This break looks like a no-op to me, but if you put code beyond the
break, you still have:

try {
   stuff();
   if (!condition()) {
     more_stuff();
   }
   catch ...

     f1: for (int i = 0; i < 100; ++i) {
             for (int j = 0; j < i; ++j) {
                 if (no_good(j)) {
                     continue f1;
                 }
             }
             cout << i << " is good!" << endl;
         }


bool is_good(i) {
   for (int j = 0; j < i; ++j) {
     if (no_good(j)) return false;
   }
   return true;
}

// What we really should be writing:

bool is_good(i) {
   return std::find(0, i, lambda(j) { no_good(j) }) == i;
}

     w1: while (cin >> ch) {
             switch(ch) {
             case 'Q': break w1;
             case '+': do_add(); break;
             default: sing(); break;
             }
         }


while (cin >> ch && process_or_quit(ch))

// process char in some thing.
// Returns true if quit char ('Q') read

bool process_or_quit(char) {
   switch (ch) {
     case 'Q': return false;
     case '+': do_add(); break;
     default: sing(); break;
   }
   return true;
}

     i1: if (c1) {
             x();
             if (c2) {
                 break i1; //----
             } // |
             y(); // |
         } else if (c3) { // |
             z(); // |
         } else { // |
             w(); // |
         } // |
         // goes here <----------


if (c1) {
     x;
     if (!c2) y();
} else if (c3) {
   z();
} else {
   w();
}

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