perl - 哈希值中的 4/16 是什么？

Question

if (%hash){
     print "That was a true value!\n";
}

That will be true if (and only if) the hash has at least one key-value pair.

The actual result is an internal debugging string useful to the people who maintain Perl. It looks something like "4/16," but the value is guaranteed to be true when the hash is nonempty, and false when it's empty. --Llama book

4/16 是什么？谁能告诉我一个小程序，从中我可以看到结果是 4/16？

Answer 1

来自perldoc perldata :

If you evaluate a hash in scalar context, it returns false if the hash is empty. If there are any key/value pairs, it returns true; more precisely, the value returned is a string consisting of the number of used buckets and the number of allocated buckets, separated by a slash. This is pretty much useful only to find out whether Perl's internal hashing algorithm is performing poorly on your data set. For example, you stick 10,000 things in a hash, but evaluating %HASH in scalar context reveals "1/16" , which means only one out of sixteen buckets has been touched, and presumably contains all 10,000 of your items.

因此，4/16 将是已使用/已分配的存储桶计数，类似以下内容将显示此值:

%hash = (1, 2);
print scalar(%hash); #prints 1/8 here