Re^4: Referring to an array without copying to a separate variable first

> ... but B::Deparse seems to know what's going on: ...

B::Deparse can't help here, cause it's a runtime error and not a syntax problem.

> ... I suspect the ; after $res is the key ...

The ';' you are seeing is an indicator that %{ } and alike are effectively do { } blocks plus dereferencing.

lanx@nc10-ubuntu:~$ perl -e '$r={a=>1};print %{$r;},"\n"'
a1
lanx@nc10-ubuntu:~$ perl -MO=Deparse,p -e '$r={a=>1};print %{$r;},"\n"
+'
$r = {'a', 1};
print %{$r;}, "\n";
-e syntax OK
lanx@nc10-ubuntu:~$ perl -MO=Deparse,p -e 'print %{ $r={a=>1};$r; },"\
+n"'
print %{$r = {'a', 1};
$r;}, "\n";
-e syntax OK
lanx@nc10-ubuntu:~$ perl -e 'print %{ $r={a=>1};$r; },"\n"'
a1
[download]

Interesting, well spotted! =)

UDPATE

Reminds me of this old trick to have code executed within interpolation

  DB<100> print " @{ [ 1..10 ] } "
 1 2 3 4 5 6 7 8 9 10
[download]

maybe clearer

  DB<106> print " @{ $a++; [1..$a ] } "
 1 
  DB<107> print " @{ $a++; [1..$a ] } "
 1 2 
  DB<108> print " @{ $a++; [1..$a ] } "
 1 2 3
[download]

Cheers Rolf

( addicted to the Perl Programming Language)

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Re^5: Referring to an array without copying to a separate variable first by kcott (Archbishop) on Jun 30, 2013 at 05:07 UTC
Just noticed your update. I don't know how old that trick is but I do use it quite often — most recently in the last hour for checking a subroutine's arguments: `my (..., $some_scalar_ref, ...) = @_; say "... @{[$$some_scalar_ref // '<undef>']} ...";` [download] Anyway, thanks for the feedback. ++ -- Ken	[reply] [d/l]