遍历密钥％hash的结果时修改哈希是否安全？

Question

在遍历keys %hash生成的列表时修改哈希是否安全？

my $blah;
my %hash;

for my $key (keys %hash)
{
  # Some code that sets $blah....
  delete $hash{$key} if $key=~/$blah/;
}