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perlstaticconstantshashref

perl static constant hashrefs

Is it possible to declare static constant hashrefs in perl? I tried it with Readonly and Const::Fast module in the following way, but get the error message "Attempt to reassign a readonly variable" when I call the sub multiple times.

use Const::Fast;
use feature 'state';

sub test {
  const state $h => {1 => 1};
  #...
}
Solution

  • const is a function, and you're calling it every time test is called. This should do the trick.

    sub test {
   state $h;
   state $initialized;
   const $h => ... if !$initialized++;
   # ...
}

    Since $h always has a true value, we can use the following:

    sub test {
   state $h;
   const $h => ... if !$h;
   # ...
}

    Of course, you can still use the old way of doing persistent lexically-scoped variables.

    {
   const my $h => ...;

   sub test {
      # ...
   }
}