Allow String.to_integer/1 to return integer when passed integer argument

[Curtis Rock]

I propose that String.to_integer/1 return an integer rather than raising an error when passed an integer argument.

Use case: When working with Phoenix LiveView and HEEx templates, database table id values are processed as both binary values and integer values, but must be converted back to integer when writing to the database.

When String.to_integer/1 is passed an integer value, it raises an error.

We add functions in our projects to make string to integer conversion more forgiving, such as the following functions found in the elixir library

defp to_integer(integer) when is_integer(integer), do: integer

defp to_integer(integer) when is_binary(integer), do: String.to_integer(integer)

sourced from here:
https://github.com/elixir-lang/elixir/blob/79cd891eb86ecb7654a7acdb63769cfdd950a5c0/lib/ex_unit/lib/ex_unit/filters.ex#L238

[José Valim]

Hi Curtis,

All functions in String accept a string only as first argument, so I would be wary of making an exception. We could perhaps allow it in Integer.parse/2 but I am not sure if we should make an exception there either, especially when we consider there are other arguments such as base and what they should mean when an integer is given.

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[Wojtek Mach]

If your project is already using Ecto, you can also use Ecto.Type.cast/2:

iex(2)> Ecto.Type.cast(:integer, 42)
{:ok, 42}
iex(3)> Ecto.Type.cast(:integer, "42")
{:ok, 42}

(same for floats, dates, etc)

Probably best to wrap it in a more convenient function like this though:

defmodule MyApp do
  def cast!(type, term) do
    {:ok, casted} = Ecto.Type.cast(type, term)
    casted
  end
end

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