Re^2: map vs for\foreach.

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Re^3: map vs for\foreach. by MidLifeXis (Monsignor) on Mar 12, 2015 at 12:12 UTC
It isn't wrong, it is just not saying what you mean. `map` is a transformation. `for` is a loop. If I use `map`, it is understood that there are to be no modifications to the original data set (and conversely, if there are side effects, I did it wrong). If I use `for`, then there is the potential for modification of the original data. It is, for me, about clarity of intent. That is why I insist (in my code) on this usage. --MidLifeXis	[reply] [d/l] [select]
Re^4: map vs for\foreach. by LanX (Saint) on Mar 13, 2015 at 18:56 UTC
> If I use map, it is understood that there are to be no modifications to the original data set I was meditating if `map` should be changed in this respect. Questions: are there use cases where a new list is returned and the old list needs to be altered by alias? if yes, should we introduce a non aliasing default var to avoid this trap? something like `$__` or so? The usual workaround is to copy $_, like in `DB<111> @b = map {my $x=$_; ++$x} @a => (2 .. 11) DB<112> @a => (1 .. 10)` [download] Then again its pretty easy to replace `++$_` with `$_+1` and `s/x/y/` with `s/x/y/r` in current Perl versions. Not sure if there are any modifying operators left without a non-modifying counterpart. Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :)} PS: Je suis Charlie!	[reply] [d/l] [select]
Re^4: map vs for\foreach. by karlgoethebier (Abbot) on Mar 13, 2015 at 18:23 UTC
"... if there are side effects, I did it wrong" Yes, yes. But you can do what you want: You get the side effect for free - even if you don't want it. `#!/usr/bin/env perl use strict; use warnings; use Data::Dump; my @original_data_set = ( 1 .. 10 ); dd \@original_data_set; my @modified_data_set = map { ++$_ } @original_data_set; dd \@original_data_set, \@modified_data_set; __END__ karls-mac-mini:monks karl$ ./1119774.pl [1 .. 10] ([2 .. 11], [2 .. 11])` [download] Best regards, Karl «The Crux of the Biscuit is the Apostrophe»	[reply] [d/l]
Re^5: map vs for\foreach. by MidLifeXis (Monsignor) on Mar 13, 2015 at 18:27 UTC
I think, in this case, that we are firmly entrenched in opposite camps, and will just have to agree to disagree. :-) --MidLifeXis	[reply]
Re^6: map vs for\foreach. by LanX (Saint) on Mar 13, 2015 at 18:44 UTC
Re^3: map vs for\foreach. by Your Mother (Archbishop) on Mar 11, 2015 at 21:48 UTC
So why is map { ++$_ } @foo; wrong? If for no other reasons: it’s a little harder to follow and four characters more typing than `$_++ for @foo`. Superstition makes me post-increment; I think it’s not slower anymore but was back in the dinosaur age. (Update: `map $_++, @foo` is a little shorter too…)	[reply] [d/l] [select]
Re^4: map vs for\foreach. by ikegami (Patriarch) on Mar 13, 2015 at 17:39 UTC
Superstition makes me post-increment; I think it’s not slower anymore but was back in the dinosaur age. Post-increment is necessarily slower since it requires making a copy of the scalar that pre-increment doesn't. However, Perl replaces post-increment operators in void context with pre-increment operators. `$ perl -MO=Deparse -e'$_++ for @a;' ++$_ foreach (@a); -e syntax OK $ perl -MO=Deparse -e'map { $_++ } @a;' map {$_++;} @a; -e syntax OK` [download]	[reply] [d/l]
Re^5: map vs for\foreach. by karlgoethebier (Abbot) on Mar 13, 2015 at 18:31 UTC
BTW: `#!/usr/bin/env perl use strict; use warnings; use Data::Dump; my @original_data_set = ( 1 .. 10 ); dd \@original_data_set; my @modified_data_set = map { $_++} @original_data_set; dd \@original_data_set, \@modified_data_set; __END__ karl-mac-mini:monks karl$ ./1119980.pl [1 .. 10] ([2 .. 11], [1 .. 10])` [download] Best regards, karl «The Crux of the Biscuit is the Apostrophe»	[reply] [d/l]
Re^6: map vs for\foreach. by LanX (Saint) on Mar 13, 2015 at 18:38 UTC


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