Lua的LazyTable实现

local ngx_req = {
      headers = function()
          return "testcase"
      end,
      method = function()
          return "GET"
      end,
}


local lazy_tbl
lazy_tbl = function(tbl, index)
  return setmetatable(tbl, {
    __index = function(self, key)
      for k,v in pairs(index) do
          print(k, v)
      end
      --print(key)
      for k,v in pairs(self) do
          print(k, v)
      end
      local fn = index[key]
      if fn then
        do
          --此处fn(self)和fn()，传入self形参与否的效果是一样，table中的匿名函数
          --定义是没有参数的，这个形参是moonscript翻译后加上去的。
          local res = fn(self)
          --local res = fn(self)        
          local res = fn()
          self[key] = res
          --实际把return res去掉也不会影响这个程序的运行结果， 在此函数中
          --从了这个return语句再也没有return调用了，而设定工作在self[key] = res这句就已经完成。
          return res
        end
      end
    end
  })
end


local build_request
build_request = function(unlazy)
  if unlazy == nil then
    unlazy = false
    --unlazy = true
  end
  do
    local t = lazy_tbl({ }, ngx_req)
    if unlazy then
      for k in pairs(ngx_req) do
        --这里遍历的ngx_req，但是调用的函数是t的。
        local _ = t[k]
      end
    end
    return t
  end
end


req = build_request("unlazy")


for k,v in pairs(req) do
    print(k, v)
end

__index = function(self, key)
 lazy_tbl({ }, ngx_req)

do 
   local tmp = 1
end 
print(tmp)

do 
   tmp = 1
end 
print(tmp)

local test 
test = function()
    do  
        local tmp = "do end"
        return tmp 
    end 
    return "ret"
end

ret = test()
print(ret)

local ngx = { 
    url = function() 
        return "url"
    end,
    method = function()
        return "method"
    end,
}

local lazy

lazy = function(tbl, index)
    return setmetatable (tbl, {
        __index = function(self, key)
            print(key)
        end 
    })  
end


local build_request
build_request = function(unlazy)
        ret = lazy({}, ngx)
        for k in pairs(ngx) do
             local _ = ret[k]
        end
end

build_request("")

local ngx_request = {
  headers = function()
    return ngx.req.get_headers()
  end,
  cmd_meth = function()
    return ngx.var.request_method
  end,
  cmd_url = function()
    return ngx.var.request_uri
  end,
}

local lazy_tbl
lazy_tbl = function(tbl, index)
  return setmetatable(tbl, {
    __index = function(self, key)
      local fn = index[key]
      if fn then
        do  
          local res = fn(self)
          self[key] = res 
          return res 
        end 
      end 
    end 
  })  
end

return ngx_request

local req = require "nginx"

app:get("/hilua", function(request,id)
    ngx.say(type(req.cmd_meth))
end

local req = require "nginx"
function Route:run(router)
        local url = req.cmd_url()
        local method = req.cmd_meth()
end