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Am 21.12.2013 18:00 schröbte Dirk Laurie:

2013/12/21 Sir Pogsalot <sir.pogsalot@gmail.com>:

On Fri, Dec 20, 2013 at 2:04 PM, Dirk Laurie <dirk.laurie@gmail.com> wrote:


2013/12/20 Sir Pogsalot <sir.pogsalot@gmail.com>:


3) I'm missing something obvious that makes this a bad idea.

+1

The following pieces of code so the same.


setmetatable(a,{__pairs=tbl})
for k,v in pairs(a) do print(k,v) end
for k,v in pairs(tbl) do print(k,v) end




Hmm, I do not understand why that is bad


Because it is not unreasonable to expect that when one
does `for k,v in pairs(a) do`, `v` will be a value from `a`.
The metamethod might supply some cases where `v` is
nil, it might ignore some key-value pairs, but if you deny
me the comfort of the assertion `a[k]==v`, I will be lost.
You can have your comfort back by means of an `__index` metamethod. I sometimes use this pattern in my code (e.g. [1]). I'm not sure though if this proposal is worth the effort, it only saves three lines of code in a very special case, and since `__pairs` is called only once per for-loop there is no obvious performance advantage either. 

Philipp
[1]: https://github.com/siffiejoe/lua-class/blob/master/src/class.lua#L111