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It uses the built-in iterator to obtain the keys and values from the hash and push them unto the stack before any looping is performed.

If you want me to be more precise, no extra copying occurs.

  • The keys are copied (i.e. fresh scalars are made for the keys) since they're not found as scalars in the hash. But that has to happen no matter the interface.
  • The pointers to the scalars placed on the stack. But that has to happen no matter the interface.
$ perl -e' use v5.14; use experimental qw( for_list ); my %h = ( a => 4, b => 6 ); my $i = 0; for my ( $k, $v ) ( %h ) { if ( !$i++ ) { ++$h{a}; ++$h{b}; } say "$k:$v"; } ' a:5 b:7

In reply to Re^8: Why does each() always re-evaluate its argument? ("for_list" ) by ikegami
in thread Why does each() always re-evaluate its argument? by Darkwing

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