in reply to Re: Re: array pre-allocation trick
in thread array pre-allocation trick

The map in your example serves no purpose other than to slow it down. The (0 .. $::size-1) builds a list which is directly assignable to an array.

By adding the map in there, you are

  1. building a list
  2. breaking the list down to feed it to the map element by element
  3. the reassembling a new (identical) list before assigning it to the array.
Nah! Your thinking of Simon Templar, originally played by Roger Moore and later by Ian Ogilvy

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Re: Re: Re: Re: array pre-allocation trick
by Anonymous Monk on Nov 02, 2002 at 00:24 UTC
    True the map doesn't do much, but it's a minimal benchmark for Aristotle's suggestion: 
    my @array = map { do_stuff_with($_); $_ } 1 .. 5000;

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    I've replaced "do_stuff_with($_)" with a no-op. It didn't perform as well as the others, so that leads me to think I shouldn't pursue using map in this case.
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[d/l]
      That very much depends on your setup. map can be the faster, slower or equal variant. There's too many constraints that play a role - you can't just say "this is faster" based on a minimal benchmark because the characteristics of each looping approach lend themselves to different data structure and control flow designs. If you take a forish approach, using map instead will be awkard - but the same is true in the reverse case.

      Makeshifts last the longest.

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