Functional conditions

garecinos4

I noticed in the 1.7.4 version the condition IF to handle its own scope, and it does not allow to persist the variable inside and neither do modifications of variables, I wonder why this change

Example:
Input:
a = 23
if true, do: a = 4
Output:
a = 23

I wonder if there is any documentation about this

3 comments

#functional-programming #scopes

1 1360 3

2018-11-26 20:04:43 UTC

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peerreynders

a = 23
if(true, do: a = 4)

warning: variable "a" is unused

Note variables defined inside case, cond, fn, if and similar do not leak. If you want to conditionally override an existing variable "a", you will have to explicitly return the variable. For example:

    if some_condition? do
      atom = :one
    else
      atom = :two
    end

should be written as

    atom =
      if some_condition? do
        :one
      else
        :two
      end

Unused variable found at:

github.com/elixir-lang/elixir

Assignments from within 'if' statements

opened 10:46AM - 27 Feb 18 UTC

closed 02:49PM - 27 Feb 18 UTC

cmeiklejohn

### Precheck * Do not use the issues tracker for help or support (try Elixir …Forum, Stack Overflow, IRC, etc.) * For proposing a new feature, please start a discussion on the Elixir Core mailing list * For bugs, do a quick search and make sure the bug has not yet been reported * Finally, be nice and have fun! ### Environment * Elixir & Erlang versions (elixir --version): Erlang 19.3 release, see below for Elixir version. * Operating system: Ubuntu Linux 16.04.3, Amazon Linux amazonlinux:2017.03.1.20170812 ### Current behavior ``` template_path = "" if (config[:app] == :exlam) do template_path = Path.join(["./priv", "templates", "#{name}.eex"]) else template_path = Path.join(["#{:code.priv_dir(:exlam)}", "templates", "#{name}.eex"]) end ``` Elixir 1.7.0-dev (cbcdcb1623be11e1ff0bd0bd46cb812c563c3bbd), on Ubuntu Linux 16.04.3, template_path is set to the path of the file. Elixir 1.7.0-dev (4e3e9cefc879b9173461b5a58f766390de9f9989), on Amazon Linux amazonlinux:2017.03.1.20170812, template_path is "". Fix in code: ``` template_path = "" template_path = if (config[:app] == :exlam) do template_path = Path.join(["./priv", "templates", "#{name}.eex"]) IO.puts "path is exlam #{template_path}" template_path else template_path = Path.join(["#{:code.priv_dir(:exlam)}", "templates", "#{name}.eex"]) IO.puts "path is not exlam #{template_path}" template_path end ``` Include code samples, errors and stacktraces if appropriate. ### Expected behavior Not sure. Should assignment from within the if be supported? (This was code I found in an existing library.)

elixir/CHANGELOG.md at v1.7 · elixir-lang/elixir · GitHub

[Kernel] Raise on unsafe variables in order to allow us to better track unused variable

Release v1.7.0 · elixir-lang/elixir · GitHub

[Kernel] Raise on unsafe variables in order to allow us to better track unused variables (also known as imperative assignment / variable leakage)

Post #1

garecinos4

Thanks

Post #2

Qqwy

TypeCheck Core Team

As a side note: It is always possible to refactor such ‘assignments from within if-statements’ code to more functional code by assigning the outcome of the if-statement to something:

Post #3

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