table.insert(t, i) 和 t[#t+1] = i 有什么区别? [英] What's the difference between table.insert(t, i) and t[#t+1] = i?

问题描述

在 Lua 中，似乎有两种方法可以将元素附加到数组中:

In Lua, there seem to be two ways of appending an element to an array:

table.insert(t, i)

和

t[#t+1] = i

我应该使用哪个，为什么?

Which should I use, and why?

推荐答案

使用哪个取决于偏好和环境:由于 # 长度运算符是在 5.1 版中引入的，t[#t+1] = i 在 Lua 5.0 中不起作用，而 table.insert 从 5.0 开始就已经存在，并且可以在两者中使用.另一方面，t[#t+1] = i 只使用语言级别的运算符，而 table.insert 涉及一个函数(它有少量的开销查找和调用并依赖于环境中的table模块).

Which to use is a matter of preference and circumstance: as the # length operator was introduced in version 5.1, t[#t+1] = i will not work in Lua 5.0, whereas table.insert has been present since 5.0 and will work in both. On the other hand, t[#t+1] = i uses exclusively language-level operators, wheras table.insert involves a function (which has a slight amount of overhead to look up and call and depends on the table module in the environment).

在Lua编程的第二版中(面向Lua 5.0的第一版的更新)，Roberto Ierusalimschy(Lua 的设计者)表示他更喜欢 t[#t+1] = i，因为它更显眼.

In the second edition of Programming in Lua (an update of the Lua 5.0-oriented first edition), Roberto Ierusalimschy (the designer of Lua) states that he prefers t[#t+1] = i, as it's more visible.

此外，根据您的用例，答案可能是都不是".请参阅有关长度运算符行为的手册:

Also, depending on your use case, the answer may be "neither". See the manual entry on the behavior of the length operator:

如果数组有洞"(即其他非 nil 值之间的 nil 值)，那么 #t 可以是任何直接在 nil 值之前的索引(也就是说，它可以考虑任何这样的 nil 值作为数组的结尾).

If the array has "holes" (that is, nil values between other non-nil values), then #t can be any of the indices that directly precedes a nil value (that is, it may consider any such nil value as the end of the array).

因此，如果您正在处理有孔的数组，请使用其中任何一个 (table.insert 使用长度运算符) 可能会将您的值附加"到数组中比您想要的更低的索引.在这种情况下如何定义数组的大小取决于您，并且同样取决于偏好和环境:您可以使用 table.maxn(在 5.2 中消失但编写起来很简单)，您可以在表中保留一个 n 字段并在必要时更新它，您可以将表包装在元表中，或者您可以使用另一种更适合您情况的解决方案(在循环中，一个 循环外作用域中的局部 tsize 通常就足够了).

As such, if you're dealing with an array with holes, using either one (table.insert uses the length operator) may "append" your value to a lower index in the array than you want. How you define the size of your array in this scenario is up to you, and, again, depends on preference and circumstance: you can use table.maxn (disappearing in 5.2 but trivial to write), you can keep an n field in the table and update it when necessary, you can wrap the table in a metatable, or you could use another solution that better fits your situation (in a loop, a local tsize in the scope immediately outside the loop will often suffice).

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