Re: Bizarre behavior with debug.setupvalue() in Lua 5.3
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- Subject: Re: Bizarre behavior with debug.setupvalue() in Lua 5.3
- From: Sean Conner <sean@...>
- Date: 2015年3月27日 17:28:30 -0400
It was thus said that the Great Paul K once stated:
> Hi Sean,
>
> > print(debug.setupvalue(meta.print,1,meta))
> > name,env = debug.getupvalue(meta.print,1) -- line 16
> > When I run it with Lua 5.3, I get:
> > _ENV
> > lua-53: /tmp/t.lua:16: attempt to index a nil value (global 'debug')
>
> I get the same error in Lua 5.3 and Lua 5.2. Aren't you setting the
> first upvalue for meta.print (which is _ENV) to "meta", which replaces
> _ENV for your current code with "meta", which makes "debug" not
> available?
I would expect setting the first upvalue of meta.print() to meta would
make meta the default global environment for meta.print() and not replace
the current global environment.
This does what I expect in Lua 5.1:
meta =
{
io = io,
tostring = tostring,
select = select,
print = function(...)
io.stdout:write("HERE I AM, JH ... ")
for i = 1 , select('#',...) do
io.stdout:write(tostring(select(i,...)),"\t")
end
io.stdout:write("\n")
end
}
setfenv(meta.print,meta)
meta.print(1,2,3)
-spc (And you can test it does by adding a call to a function not in meta
in meta.print() ... )