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Re^2: Multiple Conditional Statements

by BrowserUk (Pope)
on Sep 11, 2013 at 15:14 UTC ( #1053508=note: print w/ replies, xml ) Need Help??


in reply to Re: Multiple Conditional Statements
in thread Multiple Conditional Statements

If you like a more direct approach,

That's a perfectly valid approach, but how is it "more direct"? (And "more direct" that what for that matter?)

You have:

  1. An auxiliary boolean variable;
  2. An auxiliary array (... of references which have to be taken);
  3. Two nested loops;
  4. A callback function (from a module);
  5. An array slice;
  6. n(n+1) dereferences;
  7. n(n+1)/2 comparisons;
  8. And it doesn't even short-circuit if the first two variables compared are the same.

That's the strangest definition of "more direct" I can think of :)


With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.


Comment on Re^2: Multiple Conditional Statements
Re^3: Multiple Conditional Statements
by BillKSmith (Chaplain) on Sep 11, 2013 at 19:59 UTC
    Of course I agree with all your arguments. All I meant to imply was that it directly compares the variables in question (not copies) and with very little source code. I find it very easy to understand. In general, that should trump issues of speed, memory, or namespace.
    Bill
      I find it very easy to understand. In general, that should trump issues of speed, memory, or namespace.

      Interesting justifiction. Personally, I prefer solutions that are:

      1. Clean.

        Don't create persistent, named temporaries to clutter, conflict and confuse the purpose of the code.

      2. Clear.

        Don't introduce unnecessary (and counterproductive) levels of indirection in the name of premature optimisation (avoiding copies).

        It is more expensive to takes references then dereference those references; than to make copies of simple, small scalar values:

        ($a,$b,$c,$d,$e) = 1 .. 5; cmpthese -1,{ a=>q[ my @a = ($a,$b,$c,$d,$e); ++$_ for @a;], b=>q[my @a = \($a,$b,$c,$d,$e); ++$$_ for @a; ] };; Rate b a b 525790/s -- -23% a 685872/s 30% --
      3. Concise.

        The goal of this snippet if to cross-compare a few variables with the only interest being a single boolean truth.

        Spreading that across half a dozen lines, adding named temporaries to the mix; adding a module, a callback and nested loops; and obscure indirections to derive a simple boolean does the very opposite of making things easy to understand.

      4. Simple.

        Simple means when the algorithm calls for:

        if( <some condition> ) { ## do somthing }

        the implementation (code) should reflect that. Not detract from the algorithm by introducing unneeded complexity.

      5. Efficient.

        looping to perform all 15 comparisons when the first or the second can resolve the boolean condition is just flagrant waste.


      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
        There is a maximum of only ten comparisons. By your criteria, the OP had it right in the first place. The ternary operator, with the format from the book "Perl Best Practices", cleans it slightly.
        my $match = $RB1 == $RB2 ? 1 : $RB1 == $WR1 ? 1 : $RB1 == $WR2 ? 1 : $RB1 == $TE1 ? 1 : $RB2 == $WR1 ? 1 : $RB2 == $WR2 ? 1 : $RB2 == $TE1 ? 1 : $WR1 == $WR2 ? 1 : $WR1 == $TE1 ? 1 : $WR2 == $TE1 ? 1 : 0 ;
        UPDATE: Or even
        my $match = $RB1 == $RB2 || $RB1 == $WR1 || $RB1 == $WR2 || $RB +1 == $TE1 || $RB2 == $WR1 || $RB2 == $WR2 || $RB2 == $TE1 || $WR1 == $WR2 || $WR1 == $TE1 || $WR2 == $TE1 ;
        Bill

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