in reply to References for ano subs fixed at compile time?

If a sub doesn't close over any lexicals, than I bet that refs to it will be constant. If subs close over lexicals (or represent different code), than the refs can't be constant unless the refs have non-overlapping lifespans. 

  DB> sub test(&) { my( $c ) = @_; print 0+$c,$/; return $c }
  DB> ;{ my($a,$b); test {$a}; test {$b} }
14808916
14808916
  DB> ;{ my($a,$b); my $c = test {$a}; test {$b} }
15512116
15512804
  DB> ;{ my @a; for(1..3){ my $a; push @a, test {$a} } }
15513028
15511044
15513252

[download]

- tye        

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Re^2: References for ano subs fixed at compile time? (nope)
by LanX (Saint) on Jun 18, 2013 at 21:36 UTC
    the last case is the interesting one for me, the coderef of a block at a fixed position (and therefore the same code). I don't care if other blocks get the same ref after this one gets destroyed.

    And my test with your code shows that the ref is fix if its not returned:

      DB<123> sub test(&) { my( $c ) = @_; print 0+$c,$/; return $c }

  DB<124> ;{ my @a; for(1..3){ my $a; push @a, test {$a} } }
145187472
145182504
144725160
 => ""

  DB<125> sub test(&) { my( $c ) = @_; print 0+$c,$/}

  DB<126> ;{ my @a; for(1..3){ my $a; push @a, test {$a} } }
145184216
145184216
145184216
 => ""

    [download]

    So the ref is chosen dynamically from a pool of available refs, it can be the last one if it has been released before.

    Thx! =)

    UPDATE

    OK the following code shatters all my hopes that I found an answer to an old question ...

      DB<155> sub tst2(&) { my( $c ) = @_; print &$c,":\t",0+$c,$/;return 
+$c}

  DB<156> sub tst1(&) { my( $c ) = @_; print &$c,":\t",0+$c,$/;}

  DB<157> ;{ my $b; for my $a (1..3){tst1 {$a} ; $b=tst2 {42} if $a==1
+ } }
1:    145234328
42:    145234328
2:    141318480
3:    141318480

    [download]

    it doesn't matter how tst1() deals with the coderef, any later coderef generation might bind the address and disable it for other use.

    > If a sub doesn't close over any lexicals, than I bet that refs to it will be constant.

    Nope it doesn't matter if there are closed over variables, unfortunately you loose your bet...

      DB<158> ;{ my $b; for my $a (1..3){tst1 {1} ; $b=tst2 {2} if $a==1 }
+ }
1:    141317840
2:    141317840
1:    141318608
1:    141318608

    [download]

    Cheers Rolf

    ( addicted to the Perl Programming Language)

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      Nope it doesn't matter if there are closed over variables, unfortunately you loose your bet...

      To quote myself, with emphasis added:

      If subs close over lexicals (or represent different code)

      "sub {1}" and "sub {2}" are two different subroutines, even when you use prototypes to make the "sub" keyword implied rather than explicit.

      - tye        

[reply]
        You missed the point, the different calls to sub {1} print different refs, even that 1 is always the same code and not a closed over var.

        The reason is that sub {2} reused the first ref and $b inhibits its release!

          DB<161> ;{ my $b; for (1..3){ print sub {1} ; print $b= sub {2} if $
+_==1 } }
CODE(0x86c5af0)
CODE(0x86c5af0)
CODE(0x86c5be0)
CODE(0x86c5be0)

  DB<163> ;{ my $b; for (1..3){ print 0+sub {1} ; print 0+($b= sub {2}
+) if $_==1 } }
141319216
141319216
141319552
141319552

        [download]

        Cheers Rolf

        ( addicted to the Perl Programming Language)

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