# Features

Features is an Elixir porting of [rust cargo features](https://doc.rust-lang.org/cargo/reference/features.html).

## Disclaimer

**This package is experimental!**

Unexpected behavior may happen, so please try this library and [open an issue](https://github.com/danielefongo/features/issues/new) if you find a bug 💜.

## Installation

Add `features` to your list of dependencies in `mix.exs`:

```elixir
def deps do
  [
    {:features, "~> 0.1.0"}
  ]
end
```

## Usage

On `config.exs`:

```elixir
config :features, features: [:a_feature]
```

On code:

```elixir
defmodule MyModule do
  use Features

  @doc "A doc for do_something/0 function."
  # this will enable the next function with his doc if :a_feature is in config
  @feature :a_feature
  def do_something do
    :a_feature_is_enabled

    # this will enable the next statement if :another_feature is in config
    @feature :another_feature
    :another_feature_is_enabled

    # this will enable the next statement if :another_feature is not in config
    @feature_off :another_feature
    :another_feature_is_disabled
  end
end
```

Code is automatically removed during compilation if the feature condition is not met.

A config example is the following:

```elixir
config :features, features: [:a_feature]
```
### Testing

To test featured code you have to set features property to enable runtime execution (it replaces the compile-time deletion).

On `test.exs`:
```elixir
config :features, test: true
```

On `test_helpers.exs`:

```elixir
Features.Test.start()
```

On a test:

```elixir
defmodule MyModuleTest do
  use ExUnit.Case, async: true
  use Features.Test

  featured_test "test1", features: [:a_feature, :another_feature] do
    assert MyModule.do_something() == :another_feature_is_enabled
  end

  featured_test "test2", features: [:a_feature] do
    assert MyModule.do_something() == :another_feature_is_disabled
  end

  featured_test "test3", features: [] do
    assert_raise CaseClauseError, fn -> MyModule.do_something() end
  end
end
```