Re: Long chains of objects (aka tables)

[Petite Abeille <petite.abeille@...>]

On May 17, 2014, at 7:37 PM, Coda Highland <chighland@gmail.com> wrote:

> The nil metatable hack is substantially faster than actually implementing the necessary
> logical checks (e.g. a and a.b and a.b.c).

Plus it’s not really that bad… for example:

—8<—

local function get( aTarget, ... )
  for anIndex = 1, select( '#', ... ) do
    local aKey = select( anIndex, ... )

    aTarget = aTarget[ aKey ]

    if aTarget == nil then
      break
    end
  end

  return aTarget
end


local aTable = { { 1, { 1, 2, { 1, 2, 3, { 1, 2, 3, 4, { 1, 2, 3, 4, 5, { 1, 2, 3, 4, 5, 6, { 1, 2, 3, 4, 5, 6, 7, { 1, 2, 3, 4, 5, 6, 7, 8, 9 } } } } } } } } }

for _ = 1, 10000 do
  get( aTable, 1, 2, 3, 4, 5, 6, 7, 8, 9 )
end

—>8— 

% time lua TestTable.lua 

real	0m0.034s
user	0m0.028s
sys	0m0.003s


—8<—

debug.setmetatable( nil, { __index = function() return nil end } )

local aTable = { { 1, { 1, 2, { 1, 2, 3, { 1, 2, 3, 4, { 1, 2, 3, 4, 5, { 1, 2, 3, 4, 5, 6, { 1, 2, 3, 4, 5, 6, 7, { 1, 2, 3, 4, 5, 6, 7, 8, 9 } } } } } } } } }

for _ = 1, 10000 do
  _ = aTable[ 1 ][ 2 ][ 3 ][ 4 ][ 5 ][ 6 ][ 7 ][ 8 ][ 9 ]
end


—>8— 

$ time lua TestTable.lua 

real	0m0.013s
user	0m0.007s
sys	0m0.003s


So about 3 time slower. One will not even notice in the grand scheme of things .