如何通过指定模块和方法名称在Elixir中动态调用方法? [英] How to call a method dynamically in Elixir, by specifying both module and method name?

问题描述

我想知道长生不老药中确切的方法名称是什么

I'd like to know what exactly a method name is in elixir:

array = [1,2,3]
module_name = :lists
method_name = :nth                  # this not working
module_name.method_name(1, array)   # error, undef function lists.method_name/2
module_name.nth(1, array)           # returns 1, module_name is OK. It's an atom

但是我可以在erlang中做几乎相同的事情:

But I can do almost the same thing in erlang:

A = [1,2,3].
X = lists.
Y = nth.
X:Y(1,A).  #  returns 1

我如何在长生不老药中做到这一点?

How can I do this in elixir?

推荐答案

您可以使用apply/3，它只是对:erlang.apply/3的包装.它只是调用给定的从module到arguments的数组.由于您将参数作为模块和函数名称进行传递，因此可以使用变量.

You can use apply/3 which is just a wrapper around :erlang.apply/3. It simply invokes the given function from the module with an array of arguments. Since you are passing arguments as the module and function names you can use variables.

apply(:lists, :nth, [1, [1,2,3]])
apply(module_name, method_name, [1, array])

如果您想了解有关elixir如何处理函数调用(以及其他所有内容)的更多信息，则应查看quote和unquote.

If you want to understand more about how elixir handles function calls (and everything else) you should take a look at quote and unquote.

contents = quote do: unquote(module_name).unquote(method_name)(1, unquote(array))

返回函数调用的谐音表示.

which returns the homoiconic representation of the function call.

{{:.,0,[:lists,:nth]},0,[1,[1,2,3]]}

您可以使用

You can unquote the quoted function call with Code.eval_quoted/3

{value, binding} = Code.eval_quoted(contents)

这是一个使用Enum.fetch和var的示例.

here is an example using Enum.fetch along with a var.

quoted_fetch = quote do: Enum.fetch([1,2,3], var!(item));             
{value, binding} = Code.eval_quoted(quoted_fetch, [item: 2])

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