使用“#"运算符来计算Lua中表格的长度? [英] use "#" operator to calculate the length of a table in Lua?

问题描述

当我使用#计算表的长度时，我有一个问题.例如:

I have a question when I use # to calculte the length of a table. For Example:

local t = {"a", "b"}
local t1 = {"a", nil}
print(#t)       -- 2
print(#t1)      -- 1

---

local t = {"a", "b"}
local t1 = {nil, "a"}
print(#t)       -- 2
print(#t1)      -- 2

有人可以告诉我为什么吗?

can someone tell me why it is?

推荐答案

除非定义了__len元方法，否则#运算符只能在作为序列的表上进行操作.

Unless __len metamethod is defined, # operator can only be operated on a table that is a sequence.

序列是一个表，对于某些非负整数n，其正数字键集等于{1..n}.

A sequence is, a table that, the set of its positive numeric keys is equal to {1..n} for some non-negative integer n.

在您的示例中:

local t = {"a", "b"}

t是长度为2的序列.

local t1 = {"a", nil}

等同于local t1 = {"a"}，因此t1是长度为1的序列.

is equivalent to local t1 = {"a"}, so t1 is a sequence that has a length of 1.

local t1 = {nil, "a"}

t1不是序列，因此未定义#t1.

t1 is not a sequence, so #t1 is not defined.

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