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https://github.com/mainshayne233/feature_flag
Change what Elixir functions do via configuration values
https://github.com/mainshayne233/feature_flag
Last synced: 8 days ago
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Change what Elixir functions do via configuration values
- Host: GitHub
- URL: https://github.com/mainshayne233/feature_flag
- Owner: MainShayne233
- Created: 2019-10-24T03:07:40.000Z (about 5 years ago)
- Default Branch: master
- Last Pushed: 2019-11-05T16:20:07.000Z (about 5 years ago)
- Last Synced: 2024-10-19T06:09:10.035Z (about 1 month ago)
- Language: Elixir
- Homepage:
- Size: 38.1 KB
- Stars: 6
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# FeatureFlag
[](http://travis-ci.org/MainShayne233/feature_flag)
[](https://coveralls.io/github/MainShayne233/feature_flag?branch=master)
[](https://hex.pm/packages/feature_flag)
## The What
`FeatureFlag` allows you to write functions that can have their behavior changed by setting/modifying a config value.
For instance, using `FeatureFlag`, you can define a function like so:
```elixir
defmodule MyApp do
use FeatureFlag
def math(x, y), feature_flag do
:add -> x + y
:multiply -> x * y
:subtract -> x - y
end
end
```
This function will do one of three things depending on its feature flag value. You must set this value in your config like:
```elixir
config :feature_flag, :flags, %{
# the key here is {module_name, function_name, arity}
{MyApp, :add, 2} => :add
}
```
At this point, the function would behave like so:
```elixir
iex> MyApp.math(3, 4)
7
```
At runtime, you can change feature flag value using `FeatureFlag.set/2`, like so:
```elixir
iex> FeatureFlag.set({MyApp, :add, 2}, :multiply)
:ok
```
And now the function would behave like so:
```elixir
iex> MyApp.math(3, 4)
12
```
### Boolean feature flags
If a function's feature flag will only ever be `true` or `false`, you can definie your function like so:
```elixir
defmodule MyApp do
use FeatureFlag
def get(key), feature_flag do
get_from_cache(key)
else
get_from_db(key)
end
end
```
## Use Case
The goal of this library is to ~~make Elixir less pure~~ provide an elegant and consistent mechanism for changing what a function does depending on a value that can easily be modified (i.e. a configuration value).
This could very easily be done in plain Elixir via a simple `case` statement:
```elixir
defmodule MyApp do
def math(x, y) do
case Application.fetch_env!(:my_app, :math) do
:add -> x + y
:multiply -> x * y
:subtract x - y
end
end
end
```
There's nothing wrong with this approach, and really no need to reach for anything else.
However, beyond removing a marginal amount of code, `FeatureFlag` provides a consistent interface for defining functions with this config-based branching.
## Usage
Add FeatureFlag as a dependency in your `mix.exs` file.
```elixir
def deps do
[
{:feature_flag, "~> 0.1.5"}
]
end
```
Run `mix deps.get`, then define your function:
```elixir
defmodule MyApp
use FeatureFlag
def get(key), feature_flag do
:old_database ->
get_from_old_database(key)
:new_database ->
get_from_new_database(key)
:get_from_newer_database ->
get_from_newer_database(key)
end
end
```
If you attempt to compile now, it will fail, because you need to explictly declare the feature flag value for this function in your config:
```elixir
# config/{dev,test,prod}.exs
config :feature_flag, :flags, %{
{MyApp, :get, 1} => :old_database
}
```
Then you're done! Initially, this function will simply execute the `:old_database` block. You can change this at runtime by running:
```elixir
FeatureFlag.set({MyApp, :get, 1}, :new_database)
```
## Mentions
I'd like to thank the following people who contributed to this project either via code and/or good ideas:
- [@evuez](https://github.com/evuez)
- [@zph](https://github.com/zph)
I'd also like to thank [@Packlane](https://github.com/Packlane) for giving me time to work on and share this software.