Read lua interface

Question

In lua, is there any way to read an interface file to extract name/methods/args?

I have an .idl file like this:

interface
{
    name = myInterface,
    methods = {
        testing = {
            resulttype = "double",
            args = {{direction = "in",
            type = "double"},
        }
    }
}

This is equal to the code bellow (easier to read):

interface myInterface {
  double testing (in double a);
};

I can read file, load as string and parse with gmatch for example to extract information, but is there any easy mode to parse this info?

At the end i want something (a table for example) with the interface name, their methods, result types and args. Just to know the interface that i`m working.

An example of IDL-file from microsoft site looks quite different. — Egor Skriptunoff
Is that double {{ supposed to be a single {? In that case you could just insert an = between interface and the opening { and load the file as lua code and simply run it. That would give you a table (called interface) with all the data you need, wouldn't it? — Martin Ender
Egor, looks different. But i think lua can understant this code (i think xD hahaha). If not, i can create an interface file like you sayd on link. But i must know how to parse interface — briba
buettner, this double is not a single parameter (was that your question? I dont know if i understood). Actually the interface can have multiple parameters. And i don't know how to load this an extract this information — briba
@BrenoRiba what I was saying was that your braces are mismatched. you have 5 opening { and only 4 closing }. i guess you are missing a closing brace then. there are certainly more elegant ways to do it, but if you wrote interface = { ... } and fixed that brace-mismatch, this would be perfectly valid Lua code, so you could then do interface.name or interface.methods.testing.args[0].type or whatever you want. — Martin Ender

Martin Ender Martin Ender · Accepted Answer · 2013-04-18T18:28:06

Lua has several facilities to interpret chunks of code. Namely, dofile, loadfile and loadstring. Luckily, your input file is almost valid Lua code (assuming those braces were matched). The only thing that is problematic is interface {.

All of the above functions effectively create a function object with a file's or a string's contents as their code. dofile immediately executes that function, while the others return a function, which you can invoke whenever you like. Therefore, if you're free to change the files, replace interface in the first line with return. Then you can do:

local interface = dofile("input.idl")

And interface will be a nice table, just as you have specified it in the file. If you cannot change those files to your liking, you will have to load the file into the string, perform some string manipulation (specifically, replace the first interface with return) and then use loadstring instead:

io.input("input.idl")
local input = io.read("*all")
input = string.gsub(input, "^interface", "return") -- ^ marks beginning of string
local f = loadstring(input)
local interface = f()

In both cases this is what you will get:

> require"pl.pretty".dump(interface)
{
  name = "myInterface",
  methods = {
    testing = {
      args = {
        {
          type = "double",
          direction = "in"
        }
      },
      resulttype = "double"
    }
  }
}    

> print(interface.methods.testing.args[1].type)
double

EDIT:

I just realised, in your example input myInterface is not enclosed in " and therefore not a proper string. Is that also a mistake in your input file or is that what your files actually look like? In the latter case, you would need to change that as well. Lua is not going to complain if it's a name it doesn't know, but you also won't get the field in that case.

Read lua interface

1 Answers