CODEWITHSUNDEEP
luamoonscript
Muhammad Lukman Low
Muhammad Lukman Low

Reputation: 8533

Why does io\open not work in moonscript?

Moonscript uses \ to call methods so can someone explain to me why the code below does not work:

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

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

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

Upvotes: 1

Views: 296

Answers (2)

nonchip
nonchip

Reputation: 1142

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.

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

Upvotes: 0

Etan Reisner
Etan Reisner

Reputation: 80961

The io.open function expects to get a string as the first argument but io\open (like io:open in lua itself) is actually passing the io table as the first argument. That is it is a method call.

io\open("file", "mode")/io:open("file", "mode") are syntactic sugar for io.open(io, "file", "mode").

This is why file\read! works without an explicit argument because file gets passed as the first argument to the read("file", "format") function.

Upvotes: 4

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