lua - 为什么 io\open 在moonscript 中不起作用？

Question

Moonscript 使用 \ 来调用方法，所以有人可以向我解释为什么下面的代码不起作用：

> file = io\open("mix.exs", "rb")
[string "tmp"]:1: calling 'open' on bad self (string expected, got table)

但是当你调用它来读取文件时呢？

> file\read!
"Code.ensure_loaded?(Hex) and Hex.start

Answer 1

该io.open函数期望获得一个字符串作为第一个参数，但io\open（就像io:open在 lua 本身中一样）实际上是将io表作为第一个参数传递。那就是方法调用。

io\open("file", "mode")/io:open("file", "mode")是 . 的语法糖io.open(io, "file", "mode")。

这就是为什么file\read!没有显式参数的情况下工作的原因，因为file它作为第一个参数传递给read("file", "format")函数。

Answer 2

Moonscript uses \ to call methods

to call member methods. as in a\b c, ... translates to a.b(a,c,...).

this doesn't work here because io.open is a static function (io.open(what,how)), not a member (io.open(self,what,how)).

you couldn't call io:open in Lua either. the only place where io functions allow for being called as members is when you want to read/write stdio.

but when you call it to read the file it does ?

because now it's a member method of the file. you're actually still using io.read there, but the file object has io as a metatable index, therefore allowing you to access the same function via file.read, and since file\read! translates to file.read(file) it's the same thing.

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so essentially the answer boils down to "because io:open doesn't work in Lua".