Re: tag method for dostring?
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- Subject: Re: tag method for dostring?
- From: Roberto Ierusalimschy <roberto@...>
- Date: 1998年5月12日 14:01:39 -0400 (EDT)
> I was perusing the lua 3.0 documentation, and I was looking for a tag
> method that could be overridden for tostring() and tonumber(). Do
> these exist? If not, they might be a useful addition to the language
> so that userdatas could be more easily debugged.
What you can do is to override the functions "tostring" and "tonumber",
so they can handle your special cases. A simple way to do that is as
follows:
Howtoshow = {} -- keep functions to show selected tags
old_tostring = tostring
function tostring (o) -- redefine 'tostring'
local f = Howtoshow[tag(o)]
if f then return f(o)
else return old_tostring(o)
end
end
-- supose 'tt' is a new tag, and 'foo' is
-- the function you want to use to convert
-- such objects to strings:
Howtoshow[tt] = foo
----
Notice: in Lua 3.1, you could write the above
function as (there is no need of 'old_tostring'):
function tostring (o)
local f = Howtoshow[tag(o)]
if f then return f(o)
else return %tostring(o)
end
end
-- Roberto