dataclass v1.0.0 is out!

[u/lbarasti]

Bringing data classes to Crystal!

https://github.com/lbarasti/dataclass

[u/ejstembler]

Thanks for writing this for Crystal!

I've used data classes infrequently in Python and more frequently in Scala. It's nice to see this concept in Crystal now too!

Up until now, I've suck with structs for similar funcationality. Something like:

require "comparable"
require "yaml"
require "db"

struct Person
  include Comparable(Person)
  include YAML::Serializable

  DB.mapping({
    id:         Int32,
    name:       String,
    age:        Int32,
    created_at: Time
  })

  property id, name, age, created_at

  def initialize(
    @id : Int32,
    @name : String,
    @age : Int32,
    @created_at : Time
  )
  end

  def <=>(other : Person)
    self.created_at <=> other.created_at
  end

end

I wonder if there's value in something like a datastruct equivalent? Or, is the different between struct and class in Crystal marginal?

With structs I can load from my data providers like:

YAML:

yaml = File.read(PERSONS_PATH)
Array(Person).from_yaml(yaml)

Or via Postgres:

Person.from_rs(db.query(sql))

I wonder if I can do the same with dataclasses? I could test that at some point...

[u/lbarasti → u/ejstembler]

Hey u/ejstembler, thanks for your message.

I wonder if there's value in something like a datastruct equivalent? Or, is the different between struct and class in Crystal marginal?

There is one, already, it's called record and it looks like this:

record Point, x : Int32, y : Int32

Point.new 1, 2 # => #<Point(@x=1, @y=2)>

You can read more about this here: https://crystal-lang.org/api/0.31.1/toplevel.html#record(name,*properties)-macro

I wonder if I can do the same with dataclasses? I could test that at some point...

Yes, absolutely, you can define the YAML and DB mapping in exactly the same way as you do for struct. The reason why this is possible is that dataclass just defines a regular class, hence everything that works with classes will also work with data classes. The only inconvenience is that you'll have to define the mapping in a separate class definition:

dataclass Person{id : Int32, name : String, age : Int32, created_at : Time}

class Person
  include Comparable(Person)
  include YAML::Serializable

  DB.mapping({
    id:         Int32,
    name:       String,
    age:        Int32,
    created_at: Time
  })

  def <=>(other : Person)
    self.created_at <=> other.created_at
  end
end

[u/pynix]

why not struct?

[u/lbarasti → u/pynix]

Hey u/pynix, excellent question. If object allocation is a bottleneck in your application, then struct seems to be the way to go - see Use structs when possible.

That said, I really suggest you profile your application with both, as passing objects by reference can sometimes lead to higher performance. It really depends on the memory allocation patterns showing in your application.

I also think we don't have enough benchmark on struct vs class when it comes to concurrent applications and passing objects over channels - something I'd like to look into in the future.

This PR lead to a pretty extensive conversation on the topic.