lua中表键周围的方括号有什么作用？

Question

我碰到了像这样的桌子，键周围有方括号。我知道使用lua不需要使用lua ..使用方括号时有什么区别吗？

        local commands_json =
        {
            ["request"] = {
                ["application"] = PW_APPLICATION,
                ["push_token"] = deviceToken,
                ["language"] = "en",  --OR: system.getPreference( "ui", "language" ),
                ["hwid"] = system.getInfo("deviceID"),
                ["timezone"] = -3600,  --offset in seconds
                ["device_type"] = deviceType
            }
        }

Answer 1

它只是在表中指定键的长形式。您可以在[]（除了nil. 和浮点 NaN 之外）之间放置任何值。而没有它们，您只能使用标识符。

例如：

tbl =
{
  key name = 5,
}

这是一个编译错误，因为“键名”不是标识符（由于空格）。这有效：

tbl =
{
  ["key name"] = 5,
}

和这个：

tbl =
{
  "key name" = 5,
}

Is also a compile error. If Lua sees a naked value like this, it thinks you're trying to add to the array part of the table. That is, it confuses it with:

tbl =
{
  "key name",
}

Which creates a 1-element array, with tbl[1] equal to "key name". By using [], the compiler can easily tell that you meant for something to be a key rather than the value of an array element.

The long form also lets you distinguish between:

local name = "a name";

tbl =
{
  ["name"] = 5,
  [name] = 7,
}

The second part means to evaluate the expression name, the result of which will be the key. So this table has the keys "name" and "a name".