This feels wrong

[Steven Schveighoffer via Digitalmars-d]

On 2/2/16 4:44 AM, Shachar Shemesh wrote:
> Please consider the following program:
> import std.stdio;
>
> struct A {
>      int opApply( scope int delegate(int) dg ) {
>          foreach(int i; 0 .. 50) {
>              try {
>                  int res = dg(i);
>                  if( res!=0 ) {
>                      writefln("Delegate returned %s", res);
>                      return res;
>                  }
>              } catch(Exception ex) {
>                  writefln("Caught in loop: %s", ex.msg);
>              }
>          }
>
>          return 0;
>      }
> }
>
> void main() {
>      try {
>          A a;
>          foreach(i; a) {
>              writefln("Loop got %s", i);
>
>              if( i==10 ) {
>                  throw new Exception("Excccption");
>              }
>
>              if( i==20 ) {
>                  break;
>              }
>          }
>      } catch( Exception ex ) {
>          writefln("Caught outside of loop: %s", ex.msg);
>      }
> }
>
> When run, I expected the loop to break after 10 iterations due to the
> exception being thrown. Instead, the loop continued.
>
> The problem with this is that, sometimes, the task generating the loop
> might, itself, require exception handling. Distinguishing between the
> exceptions thrown inside the delegate and outside it becomes a somewhat
> tricky exercise.
>
> At the very least, I think this behaviour should be documented.
>
> Thoughts?

Just put try around the opApply specific parts you want to monitor. 
Don't guard the call to dg.

-Steve