Mapping..... (Was Stonehenge)

[Gary Ansok]

Brent Fulgham wrote:
> Anyway, Perl 5.6 apparently changes things a bit so you can't modify an
> unnamed
> construct list (which is basically a constant) in-place.   So the fix is to
> say:
> 
> my $bar = join "|", map { my $val = $_; chop $val; $val}
> (
>         "anathema", "bema", "carcinoma", "charisma", "diploma",
>         "dogma", "drama", "edema", "enema", "enigma", "lemma",
>         "lymphoma", "magma", "melisma", "miasma", "oedema",
>         "sarcoma", "schema", "soma", "stigma", "stoma", "trauma",
>         "gumma", "pragma",
> );

Which is another way of saying

my $bar = join "|", map { substr $_, 0, -1 }
( ... list ... )

Benchmarking shows that the substr() version is about 50% faster
than the chop() version -- and I think the substr() version is 
easier to understand, too.

The old chop() version (without the temporary) was pretty close to
the substr() version -- I showed substr() just a little faster, but
wouldn't be surprised if chop() was faster in a different environment.

Even easier to understand might be { substr $_, 0, length($_) - 1 },
but that does impose a speed penalty and isn't nearly as Perlish.

> Which just introduces a new temporary variable.  Is it less efficient?  Who
> knows.

That's what Benchmark.pm is for!

Benchmark: timing 100000 iterations of chop, regexp, sublen, subneg...
      chop: 13 wallclock secs (12.51 usr +  0.00 sys = 12.51 CPU) @
7994.88/s (n=100000)
    regexp: 14 wallclock secs (13.28 usr +  0.00 sys = 13.28 CPU) @
7531.25/s (n=100000)
    sublen: 10 wallclock secs ( 9.60 usr +  0.00 sys =  9.60 CPU) @
10413.41/s (n=100000)
    subneg:  7 wallclock secs ( 7.88 usr +  0.00 sys =  7.88 CPU) @
12687.14/s (n=100000)

(regexp was { /(.*).\z/ }; sublen was { substr $_, 0, (length($_) - 1)
})

> I sent a funny e-mail to Damian about the fix:
> 
> --------------------------------
> Tension mounting.  Stress.
> Broken Coy is bad karma!
> Where can I find peace?
> 
> It seems that Perl five
> point six broke your Coy module.
> Attached is a patch.
> 
> You will, no doubt, need
> to make it harmonious
> with the rest of Coy.
> 
> Water falls on a rock.
> A small gift from neophyte
> to the great teacher.
> 
> ---------------------------------
> 
> It was a great honor to get an e-mail back from him
> later this same day:
> 
> When the student can
> patch the teacher's broken code,
> who is the master?
> 
> Many thanks, grasshopper.
> 
> Damian

LOL!

-- Gary