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Re^3: Best practice or cargo cult?

by ikegami (Pope)
on Jun 20, 2006 at 16:24 UTC ( #556451=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Best practice or cargo cult?
in thread Best practice or cargo cult?

but I do not believe that assembling your own style by considering various options and choosing those which you consider to be the best for you would be CC

Definitely. That's why I said "the real question is whether the style was created with thought".

they all come at the expense of changing the regex semantics to be different from the standard/default semantics.

"standard/default"? They're not the same. Personally, I use the modifiers only when needed. I need s more often than not, so my standard usage is with s, which is not the default. From what I see, when people don't use s on a regexp that uses ., it rarely would cause no harm to use s, and it's often an error not to use s.

When there are defined standards and well-known semantics, I find it much better to stick with them where possible and only deviate when needed rather than making deviation the default.

When there are defined standards and well-known semantics, I'd love to here about them. There's obviously differences in the standard usage of the modifiers (default vs Damian's, for example), and the semantics are far from constant.


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Re^4: Best practice or cargo cult?
by dsheroh (Parson) on Jun 20, 2006 at 18:31 UTC
    That's why I said "the real question is whether the style was created with thought"

    In that case, I misunderstood whose thought you were referring to and had taken you mean the originator of the coding style rather than the one using it.

    When there are defined standards and well-known semantics, I'd love to here about them.

    The defined standard is documented in perlre and the well-known default semantics are those which are used in the absence of any modifiers. There are certainly times when the default semantics need to be changed, thus the standard includes modifiers such as /s to alter them, but this does not change my original point that it is generally better to stick with the default (no modifiers) semantics where possible and only invoke modified semantics when there is a need to do so.

      I'm not sure what you mean by standard, because I see nothing about the standard usage of x, s and m in perlre.

      You changed from "well-known semantics" to "well-known default semantics". My point is that they're not the same. The semantics of ., ^ and $ are not well-known, since they are context-sensitive. The defaults are overriden regularly — more often than not, in my experience — so relying on the default semantics is no good. If you wanted well known semantics in your code, without loss of functionality, it would have to be done through the enforcement of xms.

      The problem is that the world on which xms can be enforced is limited, so the "well-known semantics" would only be well-known within that world. However, that's more consistency in semantics than one would enjoy otherwise.

        The default semantics are more well-known than any non-default set of semantics. That is the nature of being the default.

        I'm not arguing that the reader of code should blindly assume the default semantics apply in any given case, but rather that there is no cause to request that non-default semantics be applied in cases where the default semantics are more than adequate and, further, that most1 code out there seems to use the default semantics in most1 places. By consistently depending on non-default semantics, you may be more self-consistent, but you are less consistent with the rest of the world.

        1 I suspect that "the vast majority" would be more accurate, but I have no proof that such is the case.

Re^4: Best practice or cargo cult?
by Juerd (Abbot) on Jun 20, 2006 at 21:10 UTC

    and it's often an error not to use s.

    It is, but never forget that it can also be a bad to use /s with .. Matching \n just like any other character is not always natural; this default for . is NOT arbitrary or accidentally introduced. It actually makes sense a lot of the time, and in fact, I encounter more line based data than data that's differently delimited.

      It actually makes sense a lot of the time

      Do you have any examples? I can't think of anything realistic.

      • When dealing with line data, I'd be in a while (<FILE>) { chomp; ... } loops, so my data would never have any \n in it.

      • When dealing with data where \n is considered whitespace, it's no more special than a space, so I'd use the s modifier.

      • When dealing with multiline records, I tend to treat the data as line data — especially if I can use the flip-flop (..) operator — so my data would never have any \n in it. This is probably where I'd be least likely to use the s modifier.

      • When dealing with binary data, \n is not special, so I'd use the s modifier.

        When dealing with line data, I'd be in a while (<FILE>) { chomp; ... } loops, so my data would never have any \n in it.

        Don't forget the single string that contains multiple lines. For the same reason you sometimes want to use /m you sometimes want to match only within a certain line, and then the default . comes in very handy. The difference is that you apparently always read streams line by line, while I like to slurp files from time to time, or get the data in a way that is naturally byte oriented instead of line oriented.

        Hmm... given your realistic world of only four possibilities, /m would also never be needed, so I hope you will be able to understand the argument above :-)

        You should realise that you or I can never, ever, think of all possible ways that other people think of to use something. Some programming language designers also tried this, and their languages are very much unlike Perl. In Perl 6, some features are provided even without any certainty that they will be used, but a discussion like this one convinces me again and again that I do want those features, because not even Larry Wall can think of all the ways someone would ever use Perl. There are reasons to want to match [^\n] easily, even though you couldn't think of any, and fortunately Perl provides this feature.

        And, of course, all these unix tools that behave in exactly the same way should be some indication that even decades ago, already people thought that . matching anything but newline would be very neat!

        Juerd # { site => 'juerd.nl', do_not_use => 'spamtrap', perl6_server => 'feather' }

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