Lua:使用字符串键隐式创建表-为什么要用括号括起来? [英] Lua: implicit table creation with string keys - why the extra brackets?

问题描述

说您要创建一个Lua表，它的所有键都是有效的lua标识符.然后，您可以使用key=value语法:

Say that you want to create a Lua table, and all its keys are valid lua identifiers. Then you can use the key=value syntax:

local niceTable = { I=1, like=1, this=1, syntax=1 }

但是，如果您的字符串不是可识别的"，则必须使用['key']=value语法:

If however your strings are not "identifiable", then you have to use the ['key']=value syntax:

local operators = { ['*']="Why", ['+']="the", ['/']="brackets", ['?']='?' }

对此我有些困惑.那些括号在那里做什么?是什么意思?

I'm a bit baffled about this. What are those brackets doing there? What do they mean?

推荐答案

它们将所包含的字符串标识为结果表中的键.第一种形式，您可以考虑等于

They identify the contained string as a key in the resulting table. The first form, you could consider as equal to

local niceTable = {}
niceTable.I = 1;
niceTable.like = 1;

第二种形式等于

local operators = {}
operators['*'] = "Why";
operators['+'] = "The";

区别在于纯粹是语法糖，不同之处在于第一个使用标识符，因此它必须遵循标识符规则，例如不以数字和解释时间常数开头，第二个形式使用任何旧字符串，因此可以在运行时确定它，例如，一个不是合法标识符的字符串.但是，结果在根本上是相同的.括号的需求很容易解释.

The difference is purely syntactic sugar, except where the first one uses identifiers, so it has to follow the identifier rules, such as doesn't start with a number and interpret-time constant, and the second form uses any old string, so it can be determined at runtime, for example, and a string that's not a legal identifier. However, the result is fundamentally the same. The need for the brackets is easily explained.

local var = 5;
local table = {
    var = 5;
};
-- table.var = 5;

在这里，var是标识符，而不是变量.

Here, var is the identifier, not the variable.

local table = {
    [var] = 5;
};
-- table[5] = 5;

在这里，var是变量，而不是标识符.

Here, var is the variable, not the identifier.

这篇关于Lua:使用字符串键隐式创建表-为什么要用括号括起来?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！