how to convert a string to a function in Elixir

Question

I need to apply some functions to a map of values. The functions are around 900 function in the worst case so i created them as records in a database and load them at once to a map.This way i may create an admin page to manage all the conversion formulas ... one day...

Now I have them like this

conversion=%{"0":"Tools.Myfunc1/1","1":"Tools.Myfunc2/1",etc...}

then I need to apply/execute them in a map statement.

The problem is that they are as strings and i get this error

|>Stream.zip(conversion) |>Enum.map( fn {rawValue, formula} -> convertUsing(rawValue,formula) end) expected a function, got "myModule.Myfunc/1"

def convertUsing(value,formula) do
        {h,form}=formula
            value
            |>ieee
            |>form.()
     end

Do they all have an arity of 1 or could that change? Also, it looks like when you call the function in convertUsing you are expecting an arity of 0 which means no arguments. — Christian Di Lorenzo
– Christian Di Lorenzo, Commented Feb 2, 2016 at 15:44
arity of 1 always. If i just pass a &myFunc1/1 in the ConvertUsing , it works — ramstein
– ramstein, Commented Feb 2, 2016 at 15:44

Patrick Oscity · Accepted Answer · 2016-02-02 17:03:11Z

You could prepend a & and then use Code.eval_string/1 to evaluate the contents of the string. This will give you the desired captured function:

defmodule Conversion do
  def convert_using(value, conversions) do
    conversions
    |> Enum.map(&string_to_fun/1)
    |> Enum.reduce(value, &apply(&1, [&2]))
  end

  defp string_to_fun(str) do
    {fun, _} = Code.eval_string("&#{str}")
    fun
  end
end

Then you can do:

defmodule Tools do
  def piratize(str), do: "#{str} arr!"
  def upcase(str), do: String.upcase(str)
end

"Hello, world!"
|> Conversion.convert_using(["Tools.piratize/1", "Tools.upcase/1"])
|> IO.puts

# HELLO, WORLD! ARR!

You might want to restrict the allowed functions to a certain module that contains only trivial conversions or so, otherwise you might introduce some security risk. For example:

defp string_to_fun(str) do
  {fun, _} = Code.eval_string("&Tools.#{str}")
  fun
end

And then just store "upcase/1" and so on in the database.

naomijub · Accepted Answer · 2019-08-29 21:55:20Z

0

Does Kernal.apply combined with String.to_atom help you? This would require you to have the function implemented in the module called by apply.

apply(<Module Name>, <:string_converted_to_atom>, [<args>])

answered Aug 29, 2019 at 21:55

naomijub

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