http://qs321.pair.com?node_id=438519


in reply to Should chomping a constant always raise an error?

Personally, it makes a lot of sense. Sure if there's no need to chomp a value then it shouldn't hurt. However the function *must* be assuming the input it to be modifyied in some way otherwise you'd not pass a value to it that you expect to be modified. 
sub modify {
   chomp( $_[0] );
   # whatever else happens, you've just potentially modified $_[0]
}

modify('fred');
# What would you expect to happen to 'fred'?

my $f ="fred\n";
modify($f);
print $f;
#fred

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sub modify2 {
   # Create a copy of the input
   my $input = $_[0];
   chomp($input);
}

modify('fred');
# works now because we're not modifying the input, but a copy of it.

my $f ="fred\n";
modify($f);
print $f;
#fred\n

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Cheers!
Rick
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Re: can this be turned into a compile-time error?
by Thilosophy (Curate) on Mar 11, 2005 at 03:56 UTC 
    sub modify {
   chomp( $_[0] );
   # whatever else happens, you've just potentially modified $_[0]
}

modify('fred');
# What would you expect to happen to 'fred'?

    [download]
    Great example. For those who did not try it out, it causes a runtime exception: 
    Modification of a read-only value attempted at /tmp/t.pl line 2.

    [download]
    Can modify somehow be declared to only take a modifiable parameter, so that we can have a compile-time error (as happens with the core chomp)? 
    Can't modify constant item in modify at -e line 1, at end of line
Execution of -e aborted due to compilation errors.

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      Can modify somehow be declared to only take a modifiable parameter, so that we can have a compile-time error (as happens with the core chomp)?
      Playing Devil's Advocate, will this work? 
      chomp(foo(",",@list))

      [download]
      Don't know? How about this? 
      chomp(join(",",@list))

      [download]
      It seems, off the top of my naive head, that the argument to chomp would have to be an l-value to be guaranteed to be modifiable.

      Is that what you want?

      -QM
      --
      Quantum Mechanics: The dreams stuff is made of

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