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Re: question for perl book & magazine authors

by QM (Parson)
on Oct 21, 2005 at 14:31 UTC ( #502010=note: print w/replies, xml ) Need Help??

in reply to question for perl book & magazine authors

map and grep are not picked up as quickly by new Perl programmers as for, for several reasons.

First, new programmers will have difficulty lining up multiple actions all at once. Compare these:

my @newlist = map { $_*2 } @list; my @list; my @newlist; for my $item( @list) { push @newlist, $item * 2; }
The first example examines all values of @list (one at a time of course), multiplies each value by 2, and saves all resulting values into @newlist.

The second example is easier for a newbie to manage. It loops through @list, one at a time. Each time through, $item will hold the active value. Multiply each value by 2, and save it in @newlist.

Second, it's easier to debug the 2nd example. There are several places to breakpoint or print out intermediate results to check that the code behaves as expected. Printing out intermediate results in a map is also easy, but it has to be done carefully to avoid munging the map return values.

My point is that a newbies coming from some other languages (those without map or grep) would be more comfortable with the 2nd form. Once entrenched, they are less likely to embrace map and grep without extra incentives.

Quantum Mechanics: The dreams stuff is made of

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[Corion]: Dumu: Yes, but switching needs to be done with caution, as you might read half an UTF-8 character in binary mode, and then switch to utf8 mode...
[Corion]: Personally, I would do the decoding of data in the program and not in the filehandle
[Corion]: ambrus: Maybe a record-based file where some data is strings encoded as utf8
[Corion]: But again, I would read all data as binary and then decode from utf8
[ambrus]: Corion: that wouldn't be my guess, but I'll wait for Dumu
[Corion]: Meh. I'm now on Firefox 57 ("Quantum") and again have to remove Pocket, and reinstall the adblocker, uMatrix (because NoScript doesn't work) and silence the about:blank page to not download crap from the internet
[Corion]: Maybe I shouldn't update software ...
[ambrus]: Corion: my guess is to first read the start of the file to check what format it is out of two or more possibilities, then rewind it and handle it differently depending on the program
[ambrus]: s/program/format/
[Dumu]: ambrus: it's about testing a file for being multiple possible file formats

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