# Functional Ruby - Notes

- immutable (don't modify inputs)
- prefer stateless objects

## Prevent access to initial state
```ruby
class UserQuery
  def initialize(query)
    @query = query
  end

  def with(query)
    self.class.new(query)
  end

  def call
    query.execute
  end
end
```

Consider:
use initializer to ONLY inject dependencies
pass ALL inputs to methods
  - less coupling
  - instantiate objects once, use them numerous times
  - data (from db or external API) becomes first class
	  - make sure this is well defined so that you can compose

Object composition:

```ruby
input = { name: "Person" }

persist_person.call(
  validate.call(
    coerce.call(input)
  )
)
```

__Lazy function calling__

Partially implement function based on arguments passed in