Re: Perl oddities (s/// doesn't DWIM in map)

I still find myself being tripped up from time to time by the following, even though I should know better:

my @w= qw/ per coercer berserker / ;
print "$_\n" for map { s/er/aler/g } @w;
[download]

The above produces the output "1 2 3". To make it DWIM, one must say:

my @w = qw/ per coercer berserker / ;
print "$_\n" for map { s/er/aler/g; $_ } @w;
[download]

I've always found that odd. (Yes, I know why it works that way).

- another intruder with the mooring in the heart of the Perl

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Re^2: Perl oddities (s/// doesn't DWIM in map) by TimToady (Parson) on Mar 01, 2005 at 20:12 UTC
This can be solved much more generically in Perl 6 with mutator methods and topics: `print "$_\n" for map { .=subst(/er/, 'aler', :global) } @w;` [download] But what you're really asking for is something other than `map` here, I think...	[reply] [d/l] [select]
Re^2: Perl oddities (s/// doesn't DWIM in map) by Joost (Canon) on Mar 01, 2005 at 14:06 UTC
Good point. More generic: Having no built-in s/// that returns a modified copy is annoying. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply]
Re^3: Perl oddities (s/// doesn't DWIM in map) by heptadecagram (Novice) on Mar 01, 2005 at 15:40 UTC
True. I'd like to see a switch: `my $modified = s/$pattern/$change_to/gr;` Where `/r` stands for 'replaced', or somesuch.	[reply] [d/l] [select]
Re^4: Perl oddities (s/// doesn't DWIM in map) by Roy Johnson (Monsignor) on Mar 01, 2005 at 18:50 UTC
Would that be equivalent to `(my $modified = $_) =~ s/$pattern/$change_to/g;` [download] or `s/$pattern/$change_to/g; my $modified = $_;` [download] ? Caution: Contents may have been coded under pressure.	[reply] [d/l] [select]
Re^5: Perl oddities (s/// doesn't DWIM in map) by Joost (Canon) on Mar 01, 2005 at 20:35 UTC
Re^2: Perl oddities (s/// doesn't DWIM in map) by Roy Johnson (Monsignor) on Mar 01, 2005 at 20:18 UTC
A related oddity is that map can modify its input, in addition to generating output. That leads to the pitfall of `my @new = map { s/foo/bar/; $_ } @old; # @old is modified along with @new! # should be my @new = map { s/foo/bar/; $_ } map {$_} @old;` [download] If map couldn't modify its input, the whole "map in a void context" debate might never have happened. `for` would be used for modifying input, map would be used for generating new output. Of course, it's a tradeoff, giving up some liberty for safety. Caution: Contents may have been coded under pressure.	[reply] [d/l] [select]
Re^3: Perl oddities (s/// doesn't DWIM in map) by ikegami (Patriarch) on Mar 01, 2005 at 22:59 UTC
`my @new = map { local $_ = $_; s/foo/bar/; $_ } @old;` also avoids the problem. Probably faster than using two `map`s, too. Still ugly, unfortunately.	[reply] [d/l] [select]
Re^3: Perl oddities (s/// doesn't DWIM in map) by Aristotle (Chancellor) on Nov 19, 2005 at 09:02 UTC
I write that as `s/foo/bar/ for my @new = @old;` [download] Makeshifts last the longest.	[reply] [d/l]
Re^2: Perl oddities (s/// doesn't DWIM in map) by Roy Johnson (Monsignor) on Mar 01, 2005 at 18:03 UTC
I understand that you were just giving an example, but it looks like gratuitous chaining to me. Why not just `for (@w) { s/er/aler/g; print "$_\n"; }` [download] You might also be interested in Algorithm::Loops 'filter'. Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re^3: Perl oddities (s/// doesn't DWIM in map) by dragonchild (Archbishop) on Mar 01, 2005 at 18:33 UTC
Because that might be part of a much larger chain. Additionally, what's gratuitous in one set of eyes is natural in another's. For example, I find Java to be a gratuitous (mis)use of classes, but others, like Smalltalkers, find it to be gratuitously procedural. :-) Being right, does not endow the right to be rude; politeness costs nothing. Being unknowing, is not the same as being stupid. Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence. Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.	[reply]


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