什么是哈希的4/16? [英] What is 4/16 in hashes?

问题描述

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

当(且仅当)哈希至少具有一个时，这将是正确的 核心价值 对.

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

实际结果是内部调试字符串，对于 人们 谁维护Perl. 它看起来像"4/16" ，但值 当散列为非空时，保证为true；当散列为非空时，保证为false 它是空的. -骆驼书

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

这是什么4/16?谁能给我看一个小程序，从中我可以看到结果是4/16?

What is this 4/16? Can anyone show me a small program from where I can see that the result is 4/16?

推荐答案

来自 perldoc perldata :

如果您在标量上下文中评估哈希，则如果哈希计算返回false 是空的.如果有任何键/值对，则返回true；否则，返回true.更多的 确切地说，返回的值是一个字符串，其中包含 已使用的存储区和已分配存储区的数量，以 削减.这仅对于确定Perl是否 内部哈希算法在您的数据集上的效果不佳.为了 例如，您将10,000个东西粘贴在哈希中，但在其中计算％HASH 标量上下文显示"1/16"，表示十六分之一 桶已被触及，大概包含了您所有的10,000 项目.

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/已分配的存储区计数，如下所示将显示该值:

so, 4/16 would be the buckets used/allocated count, and something like the following will display this value:

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

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