perl - 当我在同一个散列上循环时，在 Perl 中从散列引用中删除一个键是否安全？为什么？

Question

我基本上想这样做:

foreach my $key (keys $hash_ref) {

    Do stuff with my $key and $hash_ref

    # Delete the key from the hash
    delete $hash_ref->{$key};
}

安全吗？为什么？

Answer 1

您不是迭代哈希，而是迭代 keys 返回的键列表在你开始循环之前。请记住

for my $key (keys %$hash_ref) {
   ...
}

大致相同

my @anon = keys %$hash_ref;
for my $key (@anon) {
   ...
}

从散列中删除不会导致任何问题。

each ，另一方面，确实迭代哈希。每次调用时， each返回不同的元素。然而，它仍然是安全的 delete当前元素!

# Also safe
while (my ($key) = each(%$hash_ref)) {
   ...
   delete $hash_ref->{$key};
   ...
}

If you add or delete a hash's elements while iterating over it, entries may be skipped or duplicated--so don't do that. Exception: It is always safe to delete the item most recently returned by each()