Re: Lua 5.2 Length Operator and tables (bug?)
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- Subject: Re: Lua 5.2 Length Operator and tables (bug?)
- From: Petite Abeille <petite.abeille@...>
- Date: 2012年4月16日 13:20:13 +0200
On Apr 16, 2012, at 10:31 AM, csrl@gmx.com wrote:
> For a further (related?) look try variations of print(table.unpack(table.pack(a,b[..,z]))) where some of the parameters are nil. Sometimes the unpack list contains the same nil parameters, others not.
Perhaps worthwhile mentioning that pack/unpack are mostly useful in terms of varargs.
table.pack holds an additional 'n' field, to keep track of how many effective elements there is:
http://www.lua.org/manual/5.2/manual.html#pdf-table.pack
table.pack is equivalent to the following Lua code:
local function pack( ... )
return { n = select( '#', ... ), ... }
end
print( pack( nil, nil, nil ).n )
> 3
To properly unpack a, hmmm, packed table, you need to explicitly specify it's length:
local varargs = table.pack( nil, nil, nil )
print( #varargs )
print( varargs.n )
print( table.unpack( varargs, 1, varargs.n ) )
> 0
> 3
> nil nil nil