in reply to Getting a list of aliases to selected items from a list of array references

   if( 0 == @_ ) {
        &$sub();
    } elsif( 1 == @_ ) {
        &$sub( $_[0][0] );
    } elsif( 2 == @_ ) {
        &$sub( $_[0][0], $_[1][0] );
    } elsif( 3 == @_ ) {
        &$sub( $_[0][0], $_[1][0], $_[2][0] );
    # etc to some arbitrary maximum number of arguments
    }

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and that lead me to realize that I could get what I want using eval:     eval "&\$sub( " . join( ", ", map "\$_[$_][0]", 0..$#_ ) . " )"
You could do (untested, and probably some experimentation needed to find a good cutoff point): 
if ($#_ <= 255) {
    my $lim = $#_;
    &$sub(($_[0][0],$_[1][0],$_[2][0],$_[3][0],$_[4][0],
           $_[5][0],$_[6][0],$_[7][0],$_[8][0],$_[9][0],
           ...
           $_[255]
          )[0..$lim]);
    $#_ = $lim # remove autovivified arrayrefs
} else {
    eval "&\$sub( " . join( ", ", map "\$_[$_][0]", 0..$#_ ) . " )";
}

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Re^2: Getting a list of aliases to selected items from a list of array references (unroll)
by tye (Sage) on May 17, 2004 at 03:06 UTC

    Sort of combining this idea with my idea, I could unroll the loop, perhaps reducing the performance penalty (or perhaps not): 

        my $aPush= sub { \@_ };
    my $av= [];
    while(  9 < @_  ) {
        $av= $aPush->( @$av, $_[0][0], $_[1][0], $_[2][0], $_[3][0],
            $_[4][0], $_[5][0], $_[6][0], $_[7][0], $_[8][0], $_[9][0]
+ );
        splice @_, 0, 10;
    }
    while(  2 < @_  ) {
        $av= $aPush->( @$av, $_[0][0], $_[1][0], $_[2][0] );
        splice @_, 0, 3;
    }
    $av= $aPush->( @$av, $_->[0] )   for  @_;

    [download]

    or combine more of your idea in but still not need string eval...

    - tye        

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[d/l]

      I don't like thrashing @_ because I'm weird, so how about something like this?

          my $aPush = sub { \@_ };
    my $av = [];
    for (my $index = 0;$index < @_; $index += 16) {
      my $length = $#_ - $index;
      $av = $aPush->(@$rv, ($_[$index][0],$_[$index+1][0],
              $_[$index+2][0],$_[$index+3][0],$_[$index+4][0],
              $_[$index+5][0],$_[$index+6][0],$_[$index+7][0],
              $_[$index+8][0],$_[$index+9][0],$_[$index+10][0],
              $_[$index+11][0],$_[$index+12][0],$_[$index+13][0],
              $_[$index+14][0],$_[$index+15][0]
                )[ 0..($length < 16 ? $length:15) ]
            );
    }

      [download]

      Update: After benchmarking this against what you have in the previous post, yours is definitely faster.

      antirice    
      The first rule of Perl club is - use Perl
      The       ith rule of Perl club is - follow rule i - 1 for i > 1

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[d/l]

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