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

问题描述

当我使用 # 来计算表格的长度时，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

<小时>

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

谁能告诉我这是为什么?

can someone tell me why it is?

推荐答案

除非定义了 __len 元方法，# 操作符只能对一个是序列的表进行操作.

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

一个序列是一个表，对于某个非负整数n，它的正数字键的集合等于{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.

在你的例子中:

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

t 是一个长度为 2 的序列.

t is a sequence that has a length of 2.

local t1 = {"a", nil}

等价于local t1 = {"a"}，所以t1是一个长度为1的序列.><小时>

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，所以 #t1 没有定义.

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

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