The Universe of Discourse

Clubbing someone to death with a loaded Uzi
I once had an intern who wrote wrote the following code to process a web survey form. The form input widgets were named q1, q2, and so forth:

    foreach $k (keys %in) {
            if ($k eq q1) {
                    if ($in{$k} eq agree) {
                            $count{q10} = $count{q10} + 1;
                    }
                    if ($in{$k} eq disaagree) {
                            $count{q11} = $count{q11} + 1;
                    }
            }
            if ($k eq q2) {
                    @q2split = split(/\0/, $in{$k});
                    foreach (@q2split) {
                            $count{$_} = $count{$_} + 1;
                    }
            }
            if ($k eq q3) {
                    $count{$in{$k}} = $count{$in{$k}} + 1;
            }

            ...
     }   

    if ($in{q1} eq agree) {
            $count{q10} = $count{q10} + 1;
    }
    if ($in{q1} eq disaagree) {
            $count{q11} = $count{q11} + 1;
    }

    @q2split = split(/\0/, $in{q2});
    foreach (@q2split) {
            $count{$_} = $count{$_} + 1;
    }

    $count{$in{q3}} = $count{$in{q3}} + 1;
    ...

This is the sort of mistake you expect from an intern. I chuckled and corrected him. But I've seen it several times since from non-interns.

Here's another example. I am not making this up. Whether it's more or less odious than the intern code is up to you to decide:

         foreach $location_name (%LOCATION ) {
                $location_code = $LOCATION{$location_name};

                if ($location_name eq $location ) {

                    printf FILE "$location_code\,";
                        printf FILE "%4s", "$min3\,";
                        printf FILE "%4s", "$max3\,";
                        printf FILE "%1s", "$wx3\n";

                }      

        } 

        printf FILE "$LOCATION{$location}\,";
            printf FILE "%4s", "$min3\,";
            printf FILE "%4s", "$max3\,";
            printf FILE "%1s", "$wx3\n";

        for my $k (keys %hash) {
          if ($k eq "name") {
            $hash{$k}++;
          }
        }

It's appalling how many supposedly professional programmers see nothing wrong here. They squint at the code, and say "I think you need parentheses around %hash there", or they criticize the choice of variable names.

I first used this as an interview question because the Python code sample submitted by a job applicant contained an example of it. "Weird," I thought, "but maybe she's outgrown that." Since she claimed to be an expert Perl user, I asked her about it in Perl, using code like the example above. After she made a syntactic suggestion, I said "It's not a syntax problem, and it's not a trick question." She criticized the syntax some more. Finally I told her the answer: "Couldn't you just use $hash{name}++?"

"Oh, yeah, I guess so," she said.

A few minutes later we were going over her Python code sample and I pointed out the place where she had done the exact same thing, and asked if she was happy with that loop and wanted to change it. No, she thought it was just fine.

"Doesn't this look like the example I showed you on the whiteboard a little while ago?"

"Oh, I guess it does."

We didn't hire her.

Larry Wall once said that iterating over the keys of a hash is like clubbing someone to death with a loaded Uzi.

I had already realized that you could, in principle, commit this error with a regular array instead of with a hash, but I had never seen an example until today's episode of the Daily WTF. The Daily WTF code is so awful, all the way through, that I was afraid that people might miss this slightly-more subtle gem lurking in the middle, and that was what motivated me to write this article in the first place. Here's the gem:

        // Java
        for (int a=1;a<=params.size();a++) switch (a)
            {
              case 1 : if (params.get(0) != null) 
                this.one=params.get(0).toString();
                break;
              case 2 : if (params.get(1) != null)
                this.two=params.get(1).toString();
                break;
              ...
              case 14 : if (params.get(13) != null)
                this.fourteen=params.get(13).toString();
                break;
            }
          }

[ Addendum 20080201: A bit more. ]

[ Addendum 20090213: A counterexample. ]

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