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]

In reply to Re^5: Accidentally creating hash elements with grep { defined } on a hash slice by ikegami
in thread Accidentally creating hash elements with grep { defined } on a hash slice by ferment

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