映射varargs函数lua

我希望能够映射具有多个参数的函数，如

    function(a, b) return a+b end

放在桌子上，这样我就可以写

    answer = varmap(function(a, b) return a+b end, {1, 7, 3}, {5, 4, 8}

---

但是我对lua Varags和wikibooks上的使用

表.getn

感到不舒服，当你用

#

替换它们时，它不起作用并返回“

尝试在本地'a'（一个空值）

”上执行算术运算。

也许你正在寻找这样的东西：

function varmapn(func, ...)
   local args, result = { ... }, {}
   for arg_i = 1, #(args[1]) do
      local call_args = {}
      for arg_list = 1, #args do
         table.insert(call_args, args[arg_list][arg_i])
      end
      table.insert(result, func(table.unpack(call_args)))
   end
   return result
end

样本交互：

> answer = varmapn(function (a, b) return a+b end, {1, 7, 3}, {5, 4, 8})
> print(answer)
table: 0x970eb0
> for i = 1, 3 do print(answer[i]) end
6
11
11

> answer = mapn(function (a, b) return a+b end, {x=1, y=7, z=3}, {x=5, y=4, z=8})
> for k,v in pairs(answer) do print(k .. " = " .. v) end
z = 11
y = 11
x = 6
> answer = mapn(function (a, b) return a+b end, {1, 7, 3}, {5, 4, 8})
> for i = 1, 3 do print(answer[i]) end
6
11
11

或者，这里有一个更复杂的函数，它更一般。对于参数列表，它采用数组，或采用具有任意键的表：

function mapn(func, ...)
   local args, call_args = { ... }, {}
   local result = {}

   for k in pairs(args[1]) do
      call_args[k] = {}
   end   

   for arg_list, v in pairs(args) do
      for k in pairs(args[1]) do      
         table.insert(call_args[k], v[k])
      end
   end
   for k, v in pairs(call_args) do
      result[k] = func(table.unpack(v))
   end
   return result
end

样本交互：

> answer = varmapn(function (a, b) return a+b end, {1, 7, 3}, {5, 4, 8})
> print(answer)
table: 0x970eb0
> for i = 1, 3 do print(answer[i]) end
6
11
11

> answer = mapn(function (a, b) return a+b end, {x=1, y=7, z=3}, {x=5, y=4, z=8})
> for k,v in pairs(answer) do print(k .. " = " .. v) end
z = 11
y = 11
x = 6
> answer = mapn(function (a, b) return a+b end, {1, 7, 3}, {5, 4, 8})
> for i = 1, 3 do print(answer[i]) end
6
11
11

用法：

local arr = table.imap(function (a, b) return a+b end, {1, 7, 3}, {5, 4, 8})

还有一种可能性：

local unpack = table.unpack or unpack

--------------------------------------------------------------------------------
-- Python-like zip() iterator
--------------------------------------------------------------------------------

function zip(...)
  local arrays, ans = {...}, {}
  local index = 0
  return
    function()
      index = index + 1
      for i,t in ipairs(arrays) do
        if type(t) == 'function' then ans[i] = t() else ans[i] = t[index] end
        if ans[i] == nil then return end
      end
      return ans
    end
end

--------------------------------------------------------------------------------

function map(f,...)
  assert(type(f) == 'function','Function expected for 1st arg')
  local t = {...}
  return coroutine.wrap(
         function()
           for t in zip(unpack(t)) do
             coroutine.yield(f(unpack(t)))
           end
         end)
end

--------------------------------------------------------------------------------
-- Example use

for item in map(function(a, b) return a+b end, {1, 7, 3}, {5, 4, 8}) do
  print(item)
end

print()

for item in map(function(a) return a*2 end, {1, 7, 3}) do
  print(item)
end

---

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