Next Iterator versus Ipairs for iteration in Lua arrays.

nextvsipairs.lua

-- Evaluates times
local function time(nm,times, f,...)
  local st = os.clock()
  for i = 1, times do
    f(...)
  end
  local et = os.clock()
  print(('(%s): Times (%d): %.2f ms')
    :format(nm, times, (et-st)*1000))
end

-- next iterator
local function test_ntk(t)
  for i,v in next,t do
  end
end

-- next iterator, localized
local _next = next
local function test_lntk(t)
  for i,v in _next,t do
  end
end

-- Ipairs iterator
local function test_ipairs(t)
  for i,v in ipairs(t) do
  end
end

-- Ipairs iteratork, localized
local _ipairs = ipairs
local function test_lipairs(t)
  for i,v in _ipairs(t) do
  end
end

-- Makes a table of 'len' entries
local function make_table(len)
  local t = {}
  for i = 1,len do
    t[i] =i
  end
  return t
end

local t = make_table(1e5)
local reps = 100
time(' ltknil', reps, test_lntk, t)
time('  tknil', reps, test_ntk, t)
time('lipairs', reps, test_ipairs, t)
time(' ipairs', reps, test_lipairs, t)

lua -e "io.stdout:setvbuf 'no'"
( ltknil): Times (100): 1275.00 ms
( tknil): Times (100): 1264.00 ms
(lipairs): Times (100): 1396.00 ms
( ipairs): Times (100): 1438.00 ms
Exit code: 0

lua -e "io.stdout:setvbuf 'no'"
( ltknil): Times (100): 2525.00 ms
( tknil): Times (100): 2531.00 ms
(lipairs): Times (100): 2800.00 ms
( ipairs): Times (100): 2889.00 ms
Exit code: 0