Re: Preparing the Way
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- Subject: Re: Preparing the Way
- From: Edgar Toernig <froese@...>
- Date: 2001年2月03日 01:23:22 +0100
Hi,
Jean-Claude Wippler wrote:
>
> Let's take Edgar Toernig's note in http://froese.exit.de/sol/
> Diffs2Lua :
>
> Tags are completely gone. Instead, each object
> has an attached method table.
>
> [...]
>
> Advantages: 1) No special interface needed for tag methods.
> 2) Object data and its methods are seperated. No need to
> copy all methods into each object. 3) Every datatype has
> methods. They mustn't be emulated with set/gettable.
>
> Wouldn't the following standard Lua code solve this?
>
> local vtable = {
> _tag_ = newtag(),
> times = function (self,i) return self.v * i end,
> hello = function () return "hi!" end,
> }
>
> settagmethod(vtable._tag_, "index",
> function (x,i) return %vtable[i] end)
>
> t = {}
> settag(t, vtable._tag_)
>
> t.v = 111
>
> assert(t.v == 111)
> assert(t.none == nil)
> assert(t:times(222) == 24642)
> assert(t.hello() == "hi!")
Not at all. '.' and ':' access _different_ tables (r/w).
And, you missed the first and third point ;-) An examples:
x = File.open("foo")
x:write("Hello World!\n")
The x is a userdata. Its method table is File and x:write ==
File.write, a normal function. No magic involved. You can
redirect/overload the write function, add your own high-level
functions, ...
function File.printf(file, args[])
file:write(format(args[]))
end
x:printf("%4x", 48879)
function printf(args[])
File.stdout:print(args[])
end
printf("The answer is '%d'!", 42)
And don't forget, it's less code, simpler handling and same
speed :-)
Ciao, ET.
PS: another one? Let's make File callable. Calling it will
open a file:
methods(File, {}) # File gets its own methods
function File:call(tbl, name, mode) # and the call method
return tbl.open(name, mode)
end
x = File("tmp", "w")