Re: __index and function args
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- Subject: Re: __index and function args
- From: Andreas Stenius <kaos@...>
- Date: 2006年10月03日 08:32:10 +0200
Wesley Smith skrev:
Let's say I have
Obj = {}
Obj_mt = { __index = function(t, k) -- do something
end
}
function Obj.new(o)
setmetatable(o, Obj_mt)
return o
end
obj1 = Obj.new{}
obj1:draw_circle(0, 0, 0.5)
When draw_circle is called, it looks up __index and falls the function
defined in the metatable above where t = obj1 and k = "draw_circle".
My question is, how do I get at the arguments? What happens to 0, 0,
0.5 and how can I access them?
thanks,
wes
What you could do is to return a anonymous (lambda) function that calls
the requested function. That might not be what you need in this case,
but was usefull for me when implementing XML-RPC.
function Obj_mt.__index(t, k)
return function(...)
-- the function name to call is in `k'
-- `...' is the arguments passed to this function
-- dummy example
if k == "draw_circle" then
return my_draw_circle_impl(...)
else
return nil, "unknown function"
end
-- or, another dummy example
return my_func_impl[k](...)
-- where my_func_impl probably should have a metatable
-- returning a default function for undefined k's giving
-- a descriptive error message
end
end
Another meta method to look at is __call, which can be quite nice :)
Cheers,
Andreas