Re: __pairs metamethod - is it in?
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- Subject: Re: __pairs metamethod - is it in?
- From: Mark Hamburg <mhamburg@...>
- Date: 2005年2月03日 16:26:19 -0800
I'm not sure I've seen a concrete proposal, so here goes:
local raw_next = next
local raw_ipairs = ipairs
pairs = function( t )
local mt = getmetatable( t )
local mt_pairs = mt and mt.__pairs
if mt_pairs then
return mt_pairs( t )
else
mt_next = ( mt and mt.__next ) or raw_next
return mt_next, t
end
end
next = function( t, k )
local mt = getmetatable( t )
local next_imp = ( mt and mt.__next ) or raw_next
return next_imp( t, k )
end
ipairs = function( t )
local mt = getmetatable( t )
return ( ( mt and mt.__ipairs ) or raw_ipairs )( t )
end
This actually needs to be C code so that it can see protected metatables.
It's a little ugly having to patch both __pairs and __next, but so it goes.
In fact, one could argue that all of the standard table manipulation
routines should support this approach with the old versions potentially
exported in a rawtable namespace. So, consider the point argued.
The argument for adding these metamethods is that they work in support of
Lua's use of proxy tables.
Is there a strong against adding these metamethods?
I do go both ways on whether to export all of the raw routines. In
particular, pairs and table.foreach can be used to discover keys that one
might want to keep undiscoverable.
Mark