[](CODE_OF_CONDUCT.md)
# Conditional Child
A wrapper for starting and stopping a child process in runtime, based on periodic checks.
A common use case is to start and stop processes when feature flags are toggled, but any condition can be used.
## Installation
Add `conditional_child` to your list of dependencies:
```elixir
def deps do
[{:conditional_child, "~> 0.1"}]
end
```
## How to use
Suppose you have a static `Demo.Worker` child in your application supervision tree:
```elixir
defmodule Demo.Application do
@moduledoc false
use Application
@impl true
def start(_type, _args) do
children = [
Demo.Worker
]
opts = [strategy: :one_for_one, name: Demo.Supervisor]
Supervisor.start_link(children, opts)
end
end
```
To make it conditional, just wrap your child definition into a `ConditionalChild` process, passing `start_if` and `child` options, like in the diff below:
```diff
- Demo.Worker
+ {ConditionalChild, child: Demo.Worker, start_if: fn -> your_condition() end}
```
Becoming:
```elixir
defmodule Demo.Application do
@moduledoc false
use Application
@impl true
def start(_type, _args) do
children = [
{ConditionalChild, child: Demo.Worker, start_if: fn -> your_condition() end}
]
opts = [strategy: :one_for_one, name: Demo.Supervisor]
Supervisor.start_link(children, opts)
end
end
```
During initialization, `ConditionalChild` will execute `start_if` and only start the child process if it evaluates to `true`.
After that, it will execute `start_if` every second, and start/stop the process based on the result. The check interval can be changed if desired.
For more details, see [`ConditionalChild`](https://hexdocs.pm/conditional_child/ConditionalChild.html).
## Code of Conduct
This project Contributor Covenant version 2.1. Check [CODE_OF_CONDUCT.md](/CODE_OF_CONDUCT.md) file for more information.
## License
`conditional_child` source code is released under Apache License 2.0.
Check [NOTICE](/NOTICE) and [LICENSE](/LICENSE) files for more information.
