Re: [PROPOSAL] multiple keys/values with function metamethod

["Soni L." <fakedme@...>]

On 11/09/15 08:47 AM, Rodrigo Azevedo wrote:
> We can use functions as metamethods,
>
> t[k] call __index = function(t,k) end
> or
> t[k] = v call __newindex = function(t,k,v) end
>
> but in Lua functions can have multiple parameters as well as real 
> multiple return values.
>
> Proposal: extend the syntax to
>
> t[k1,k2,k3] to call __index = function(t,k1,k2,k3) end
> and
> t[k1,k2,k3] = v1,v2,v3 to call __newindex = 
> function(t,k1,k2,k3,v1,v2,v3) end
> -- maybe with local _ENV variables to specify the number of k and v
I prefer k1,v1,k2,v2,...

Also:

function(t, ...)
local kandvcount = select('#',...)
for i=1, kandvcount, 2 do
  local k, v = select(i, ...)
end
local kcount = kandvcount / 2 -- number of k = number of k+v / 2, 
because number of k = number of v.
end
> and to keep things consistent with the current syntax of assignments
>
> a,b,t[k1,k2,k3] = v1,v2,v3,v4,v5
> equals
> a = v1; b=v2; t[k1,k2,k3] = v3,v4,v5
> and
> a,t[k1,k2,k3],b = v1,v2,v3,v4,v5
> equals
> a=v1; t[k1,k2,k3] = v2; b = v3
>
> I think this really improve the syntax/simplify userdata use cases and 
> keep things consistent with Lua functions capabilities.
>
> Simple examples:
>
> "multidimensional tables"
> u[v1,v2] = v4
> will be much faster (with only one copy of all values to the stack) 
> then u[v1][v2] = v4, with two function calls and consequent copies to 
> the stack, memory allocation etc.
>
> "simple archive"
> arq["Name","Country"] = "Rodrigo","Brazil"
> is more readable (and possible fast) than
> arq.Name = "Rodrigo"
> arq.Country = "Brazil"
>
> Of course the C side must change, but if you are smart enough to write 
> a C module then you can adapt yourself.
>
>
> --
> Rodrigo Azevedo Moreira da Silva

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