I have a stringified value that may be an integer or boolean ("20", "true"). I would like to cast the value to it's type, however, when I do a conversion on the wrong type, I get a runtime error:
iex> String.to_existing_atom("20")
** (ArgumentError) argument error
:erlang.binary_to_existing_atom("20", :utf8)
iex> String.to_integer("true")
** (ArgumentError) argument error
:erlang.binary_to_integer("true")
If you need to convert only integers and booleans from strings you may do something like this:
defmodule Converter do
def convert!("true"), do: true
def convert!("false"), do: false
def convert!(num), do: String.to_integer(num)
end
Sample usage:
iex(4)> Enum.map(["20", "true", "-5", "false"], &Converter.convert!/1)
[20, true, -5, false]
If you are dealing with json you may want to consider using a parsing library such as Poison.
By definition String.to_existing_atom/1 will fail if there is no existing atom with such name. If you forcefully create atom for given string (be careful as atoms aren't GC-ed so you can DoS yourself by that) you need to use String.to_atom/1.
However if you want to parse binary and get value from it then you can use:
Take a look at WannabeBool library. Not the solution for the example, but useful to convert strings to boolean.
WannabeBool.to_boolean("true")
true
WannabeBool.to_boolean("false")
false
