Re: do some operation on a set of values

[Steve Litt <slitt@...>]

On Saturday 25 December 2010 21:52:44 Duncan Cross wrote:
> On Sun, Dec 26, 2010 at 12:32 AM, Peyman <peiman_3009@yahoo.com> wrote:
> >> Learn about metatables and metamethods.
> >
> > there is no way instead of metatables ?
> 
> No.
> 
> > there is a simple sample of metatables ?
> 
>  -- create a new metatable
>  meta = {}
> 
>  -- define a function that returns a table after giving it our metatable
>  function valueset(t)
>    return setmetatable(t or {}, meta)
>  end
> 
>  -- add metamethods to our metatable that change behavior for + and *
>  function meta.__add(set1, set2)
>    local result = {}
>    for i = 1, math.min(#set1, #set2) do
>      result[i] = set1[i] + set2[i]
>    end
>    return valueset(result)
>  end
>  function meta.__mul(set1, set2)
>    local result = {}
>    for i = 1, math.min(#set1, #set2) do
>      result[i] = set1[i] * set2[i]
>    end
>    return valueset(result)
>  end
> 
>  -- test it
>  a = valueset{1, 2, 3}
>  b = valueset{5, 6, 7}
> 
>  c = a + b                --> {6, 8, 10}
>  c = a * b                --> {5, 12, 21}
> 
> 
> -Duncan

Thanks Duncan,

I have only a week or two of Lua and had been putting off metatables because 
they seemed hard to explain. Your example plus the info on 
http://lua-users.org/wiki/MetamethodsTutorial
have given me at least some idea of how metatables and metamethods can be used 
to overload arithmetic operators in Lua.

So you sped up my learning by several days. Thanks!

SteveT

Steve Litt
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