in reply to Re^4: Making a hash with lists
in thread Making a hash with lists

Oops. I thought those results looked fishy. Thanks; I've learnt something today.

(This must be quite a common mistake to make. I would have expected the "strict" pragma to pick up the scoping error, but it looks like 'strict' isn't active within the evalled code by default.)

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Re^6: Making a hash with lists
by BrowserUk (Patriarch) on Jun 28, 2008 at 19:08 UTC
    but it looks like 'strict' isn't active within the evalled code by default

    By default it isn't, due to this piece of nonsense from Benchmark.pm: 

    # evaluate something in a clean lexical environment
sub _doeval { no strict;  eval shift }

    [download]

    If you remove the no strict; as I have, then you'd have got: 

    For 10 elements:
runloop unable to compile ' my @res = zip(   @a,  @b ) ': 
Global symbol "@a" requires explicit package name at (eval 4) line 1.
Global symbol "@b" requires explicit package name at (eval 4) line 1.

code: sub { for (1 .. 1) { local $_; package main;  my @res = zip(   @
+a,  @b ) ;} }
 at c:\test\junk9.pl line 29

    [download]

    Which seems far more useful than the current behaviour. I'm not sure what the author hoped to achieve by adding it?

    The other thing to note in my version is the assignment of the result. Without this, Perl may optimise away code that appears in a void context. In 5.10 for example, map called in a void context doesn't bother stacking the results which would further skew the benchmark.

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
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