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Re^3: Why doesn't Perl provide %_ as the hash equivalent of @_ in subs? (ugly++)

by BrowserUk (Pope)
on Sep 27, 2013 at 10:01 UTC ( #1055952=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Why doesn't Perl provide %_ as the hash equivalent of @_ in subs? (ugly++)
in thread Why doesn't Perl provide %_ as the hash equivalent of @_ in subs?

Why not apply the same principle to %_?

Because $_ costs (almost) nothing to provide; so people not using it do not pay a penalty for those that do.

Setting up a hash from an arbitrary list of value would require substantial extra validation to see if doing so made any sense -- are there an even number; does the first of each pair make sense as a key etc. -- then building the hash and aliasing the hash values to the input arguments etc.

That is a substantial penalty for everyone who doesn't used that hash to pay, for the convenience of the few that would.

If you want that facility, do it yourself, cos I have no use for it and I don't want to pay the penalty.


With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
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.


Comment on Re^3: Why doesn't Perl provide %_ as the hash equivalent of @_ in subs? (ugly++)
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Re^4: Why doesn't Perl provide %_ as the hash equivalent of @_ in subs? (ugly++)
by smls (Pilgrim) on Sep 27, 2013 at 10:15 UTC

    If it would make all function calls slower, then I agree with you that it wouldn't be worth it.

    But does that really have to be the case?
    choroba suggested above that the hash could be built when first used... Would that not be technically feasible?

      Like with $&, $`, $' you would only have a performance hit if you actually used it.

        In recent versions of Perl there's virtually no performance hit using these variables any more.

        use Moops; class Cow :rw { has name => (default => 'Ermintrude') }; say Cow->new->name
      If it would make all function calls slower, then I agree with you that it wouldn't be worth it.

      3 times slower...

      sub withNames{ local %_ = @_; ++$_{$_} for keys %_; };; sub sansNames{ ++$_ for @_; };; cmpthese -1,{a=>q[ withNames( 1 .. $_*2 ) for 1..5 ], b=>q[ sansNames( + 1..$_ ) for 1 .. 5 ] };; Rate a b a 32135/s -- -75% b 127549/s 297% --
      hash could be built when first used... Would that not be technically feasible?

      Feasible, yes.

      A good idea? Sounds like a recipe for disaster to me.

      And all to save you adding local %_ = @_; where you want it. Worth the effort? Absolutely not.


      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      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.

        sub withNames{ local %_ = @_; ++$_{$_} for keys %_; };;

        Try  ++$_ for values %_;

        :P lol

        Yeah, local %_=@_; is not hard to type :)

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