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stu42j (6348)

stu42j
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Journal of stu42j (6348)

Tuesday May 13, 2008
09:07 PM

Curse of the Double Equals

[ #36412 ]

Every beginner programmer (of C-style languages) has to learn to deal with '=' (assignment) vs. '==' (comparison). Using = in an if clause is probably one of the most common early mistakes.

I'd like to think that I'm past that stage of my programming experience. However, about once a year I'll waste a couple of hours debugging to eventually notice the missing =.

I was working on some Javascript today and I had the feeling something was wrong with that if but my brain kept telling me to change the = to eq. Must be the jet lag from Ireland. Yeah, the jet lag. That's it, that's the ticket.

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  • Is there a critic policy for that yet?
    • I was about to say yes, but then I checked and, no, we don't have a policy for that. CodePro has one for Java and that's what I was thinking of. :-)

      As someone else said, I always write "10 == $x" instead of "$x == 10". It takes just a little getting used to, but it's a MUCH safer style. In autoboxed scalars, it works well too: in Java, "10".equals(str) is better than str.equals("10") because the former handles null gracefully and the latter does not.

      For consistency, I try to put the constant first for ev
  • If you're comparing a constant to a variable, then put the constant first in the expression.

    if (10 == $x)

    If you forget the extra '=' then most C-style languages will throw a compile-time error.

    Can't count the amount of time that's saved me over the last twenty years.