Re: metatable - tostring,tonumber
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- Subject: Re: metatable - tostring,tonumber
- From: Tom Wrensch <twrensch@...>
- Date: 2002年3月19日 15:03:57 -0800 (PST)
Here's a correction to my own mail:
I forgot that only tables and userdata can have metatables, so the code I
gave fails for numbers, strings, and such. To fix it the type of the
object must be checked using the type() function. So tostring might be:
_tostring = tostring
function tostring(obj)
local tsf = _tostring
if type(mt)=="table" or type(mt)=="userdata" then
local mt = metatable(obj)
if mt~=nil then
tsf = mt.tostring or tsf
end
end
return tsf(obj)
end
Perhaps it would make sense to modify the metatable function so it returns
nil for objects that are not userdatas or tables?
- Tom
On 2002年3月19日, Tom Wrensch wrote:
> On 2002年3月19日, nikdo79 wrote:
>
> > Hi there,
> >
> > there's no entry in the Metatable for tostring/tonumber?
> > I can't make a Object-Table to say it's class when being tostring'ed?
> > so that e.g.:
>
> You can add this fairly easily: (untested code)
>
> _tostring = tostring
> function tostring(obj)
> local tsf = _tostring
> local mt = metatable(obj)
> if mt~=nil then
> tsf = mt.tostring or tsf
> end
> return tsf(obj)
> end
>
> The version for tonumber is similar: (again, untested)
>
> _tonumber = tonumber
> function tonumber(obj)
> local tnf = _tonumber
> local mt = metatable(obj)
> if mt ~= nil then
> tnf = mt.tonumber or tnf
> end
> return tnf(obj)
> end
>
> Of course you can also implement these in 'C' if you need to.
>
> - Tom
>
> > myobject=Car.New{TopSpeed=160,Brand='Opel',Type='Corsa'}
> >
> > write(tostring(myobject))
> >
> > would result in:
> > Car Object: Opel Corsa, 160 km/h max
> >
> > That's right, isn't it?
> >
> > Dom
> >
> >
>
>