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my %h : shared;
$x = $h{foo};                         # R1 safe?
@x = keys(%h);                        # R2 safe?
while (($k, $v) = each(%h)) { ... }   # R3 safe?

$h{foo} = "change the existing 'foo' entry";   # W1 aka modification
$h{bar} = "add a 'bar' entry";                 # W2 aka insertion
delete($h{zoi});                               # W3 aka deletion