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digitalmars.D - Unconditional loop exists

reply "bearophile" <bearophileHUGS lycos.com> writes:
Are situations like this, that are potential signs of 
bugs/mistakes, worth reporting with warnings?


int foo() {
     // Unconditional 'break' within a loop:
     foreach (immutable _; 0 .. 10) {
         //...
         break;
     }

     // Unconditional 'return' within a loop:
     foreach (immutable _; 0 .. 10) {
         //...
         return 0;
     }

     assert(0);
}


Bye,
bearophile
Aug 13 2013
next sibling parent "monarch_dodra" <monarchdodra gmail.com> writes:
On Tuesday, 13 August 2013 at 14:56:32 UTC, bearophile wrote:
 Are situations like this, that are potential signs of 
 bugs/mistakes, worth reporting with warnings?


 int foo() {
     // Unconditional 'break' within a loop:
     foreach (immutable _; 0 .. 10) {
         //...
         break;
     }

     // Unconditional 'return' within a loop:
     foreach (immutable _; 0 .. 10) {
         //...
         return 0;
     }

     assert(0);
 }


 Bye,
 bearophile

Arguably, D has the "unreachable code" warning, so an unconditional break would short circuit the incrementation code. So I think there is no need for a "new" warning for this, but to make it detect that a certain amount of code is not reachable.
Aug 13 2013
prev sibling next sibling parent Timon Gehr <timon.gehr gmx.ch> writes:
On 08/13/2013 04:56 PM, bearophile wrote:
 Are situations like this, that are potential signs of bugs/mistakes,
 worth reporting with warnings?


 int foo() {
      // Unconditional 'break' within a loop:
      foreach (immutable _; 0 .. 10) {
          //...
          break;
      }

      // Unconditional 'return' within a loop:
      foreach (immutable _; 0 .. 10) {
          //...
          return 0;
      }

      assert(0);
 }


 Bye,
 bearophile

Well, the following is the most generic way to get the first element of some iterable: foreach(x;s) return x;
Aug 13 2013
prev sibling next sibling parent "bearophile" <bearophileHUGS lycos.com> writes:
monarch_dodra:

 Arguably, D has the "unreachable code" warning, so an 
 unconditional break would short circuit the incrementation code.

 So I think there is no need for a "new" warning for this, but 
 to make it detect that a certain amount of code is not 
 reachable.

The D compiler gives a warning if you add code after those return and break. So the missing warning is useful when those return and break are at the end of the loop body. That assert(0) is needed because D doesn't deduce that return is always executed. Bye, bearophile
Aug 13 2013
prev sibling next sibling parent "bearophile" <bearophileHUGS lycos.com> writes:
Timon Gehr:

 Well, the following is the most generic way to get the first 
 element of some iterable:

 foreach(x;s) return x;

I think I have not used that idiom even with opApply, but it's acceptable code. And perhaps someone will find a use case even for the unconditional loop break. So I think this little idea-proposal is already closed :-) Bye, bearophile
Aug 13 2013
prev sibling next sibling parent "Brian Schott" <briancschott gmail.com> writes:
If you get bored:
1. Run "dscanner --ast" on some source code
2. Create an XPath expression to find the code you don't like
3. Create a tool that checks the expression against the AST
4. Enjoy your low-budget static code analysis tool.

(This idea shamelessly stolen from PMD)

https://github.com/Hackerpilot/Dscanner/
http://pmd.sourceforge.net/pmd-5.0.5/xpathruletutorial.html
Aug 13 2013
prev sibling parent "Jonathan M Davis" <jmdavisProg gmx.com> writes:
On Tuesday, August 13, 2013 19:58:28 Brian Schott wrote:
 If you get bored:

With so much stuff to do for D, how could you ever get bored. ;) - Jonathan M Davis P.S. Keep up the good work.
Aug 13 2013