Lua-如何动态调用模块？

Question

Here's some much-simiplified Lua code I'm working with. I need to know how to dynamically call another module ('zebra'):

avar = require "avar"
bvar = require "bvar"

function create(zebra)
  print(zebra.new())
end

print(create(avar))

And here are two modules:

local Avar = {}

function Avar.new()
  return "avar"
end

return Avar

local Bvar = {}

function Bvar.new()
  return "new"
end

function Bvar.old()
  return "old"
end

return Bvar

If I try to pass in the string "avar" to my 'create' function, it doesn't work. If I pass in the word 'avar' with no quotes, it does work, however, I don't understand what avar with no quotes is? It seems to be a blank table? Not sure how to pass a blank table as an argument in my main program.

But maybe I'm totally on the wrong path. How do I dynamically call modules?

Answer 1

avar without the quotes is a global variable you created. It is initialized to the value returned by the require function ¹ , which is the value returned by the module you are invoking. In this case, its a table with the new field that happens to be a function.

¹ Importing a modules in Lua is done via regular functions instead of a special syntax. The function call parenthesis can be ommited because parens are optional if you write a function call with a single argument and that argument is a string or a table.

Other than that, there are also some other things you are confusing here:

• The table you are storing on avar is not empty! You can print its contents by doing for k,v in pairs(avar) do print(k,v) end to see that.

• The avar , bvar and create variables are global by default and will be seen by other modules. Most of the time you would rather make them local instead.

   local avar = -- ... local bvar = -- ... local function create (zebra) -- ... end 

• The create function clearly expects a table since it does table indexing on its argument (getting the new key and calling it). The string doesn't have a "new" key so it won't work.

• You aren't really dynamically calling a module. You are requiring that module in a regular way and it just happens that you pass the module return value into a function.

• create always returns nil so there is no point in doing print(create(avar)) . You probablu want to modify create to return its object instead of printing it.

Answer 2

You can require any time:

function create(zebraModuleName)
  zebraType = require(zebraModuleName)
  print(zebraType .new())
end

print(create("avar"))
print(create("bvar"))

Answer 3

You can use standard require from lua language or build your own loader using metatables/metamethods.

1. create a global function:

function dynrequire (module)                                                                                           
  return setmetatable ({},{
    __index = function (table,key)
      return require(module..'.'..key)
    end
  })
end

2. Create your project tree visible to package.path

./MySwiss/
  \___ init.lua
  \___ cut.lua
  \___ glue.lua
  \___ dosomething.lua

3. Make your module dynamic you only need to put this line on your MySwiss/init.lua (as if you were namespacing a PHP class):

return dynrequire('MySwiss')

4. Require your module and use subproperties dynamically On your script you only need to require MySwiss, and the folder file (or subfolders with dynrequire('MySwiss.SubFolderName') .

var X = require('MySwiss')
X.glue()

Note that MySwiss doesn't have glue key. But when you try access de glue key the metamethod __index try to require submodule. You can the full project tree using this technique. The only downside is the external dependencies not packed this way.