Re: Lua as Configuration Conditional Statement inside table definition

[steve donovan <steve.j.donovan@...>]

On Wed, Nov 10, 2010 at 12:08 PM, Gopalakrishnan Subramani
<gopalakrishnan.subramani@gmail.com> wrote:
> Is it possible to add anonymous function to the table and through meta
> table, I can check the type of the element added to the table.
> Enum1 = ENUMERATION {
>    {2, "Backword"},
>
>    function()
>       if BIDIERCTIONAL_SUPPORTED then
>       return {3, "BiDirectional"}
>   end,

Oh yes, that would work. You would iterate over the table and if it
was a function, evaluate it.

function ENUMERATE (spec)
  local res = {}
  for _, item in ipairs(spec) do
    if type(item) == 'function' then item = item() end
    if item then
       res[item[2]] = res[item[1]]
   end
end

Will end up with a table like so {Forward=1,Backword=2,None=4} if the
function failed.

> Thing is, it should be readable format.

Now that's the thing!  In which case, I think Luiz' format is
definitely the way to go - read up about how and/or behave in Lua.

But, there's usually always another way in Lua. Make a function that
returns the function

function cond(cond_var, item)
   return function()
      if _G[cond_var] then return item end
   end
end

Then the anonymous function in the table constructor simply becomes
cond('BIDIRECTIONAL_SUPPORTED',{3,"BiDirectional"})

The 'quoting' of the condition is important, if you want this to work
at _run-time_.  Otherwise, the condition variable is evaluated at
compile-time.

steve d.