Re^4: Accidentally creating hash elements with grep { defined } on a hash slice

Why does grep require lvalues?

So you can suprise people with what this does:

perl -e "@in = (1..5); @out = grep { $_++ } @in; print qq{@in}"
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But as far as I can tell, there is no good reason.

Oh - a good reason? Sorry, haven't got one of them. Move along please, nothing to see here.

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Re^5: Accidentally creating hash elements with grep { defined } on a hash slice by ikegami (Patriarch) on Nov 04, 2008 at 15:21 UTC
True, but it's a bad example since `@in` naturally returns lvalues. `>perl -le" @in = (1..5); @out = sort { $a=$b='!'; 0 } @in; print qq{@i +n}" ! ! ! ! !` [download] Note the absence of the "M" flag. `>perl -MO=Concise -le" @in = (1..5); @out = sort { $a=$b='!'; 0 } @in; + print qq{@in}" ... e <1> rv2av[t11] lK/1 ->f ...` [download] It will affect `pp_pos - Adds lvalue magic pp_substr - Adds lvalue magic pp_vec - Adds lvalue magic pp_aelem - Extends array pp_aelemfast - Extends array pp_aslice - Extends array pp_helem - Extends hash pp_hslice - Extends hash pp_padsv - No effect as far as I can tell pp_rv2sv - ??? pp_rv2av - ??? pp_rv2gv - ???` [download]	[reply] [d/l] [select]

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Re^5: Accidentally creating hash elements with grep { defined } on a hash slice
by ikegami (Patriarch) on Nov 04, 2008 at 15:21 UTC

True, but it's a bad example since @in naturally returns lvalues.

>perl -le" @in = (1..5); @out = sort { $a=$b='!'; 0 } @in; print qq{@i
+n}"
! ! ! ! !
[download]

Note the absence of the "M" flag.

>perl -MO=Concise -le" @in = (1..5); @out = sort { $a=$b='!'; 0 } @in;
+ print qq{@in}"
...
e              <1> rv2av[t11] lK/1 ->f
...
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It will affect

pp_pos       - Adds lvalue magic
pp_substr    - Adds lvalue magic
pp_vec       - Adds lvalue magic
pp_aelem     - Extends array
pp_aelemfast - Extends array
pp_aslice    - Extends array
pp_helem     - Extends hash
pp_hslice    - Extends hash
pp_padsv     - No effect as far as I can tell
pp_rv2sv     - ???
pp_rv2av     - ???
pp_rv2gv     - ???
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