[ruby-core:106677] [Ruby master Feature#15192] Introduce a new "shortcut assigning" syntax to convenient setup instance variables

Issue #15192 has been updated by austin (Austin Ziegler).


Dan0042 (Daniel DeLorme) wrote in #note-26:
> austin (Austin Ziegler) wrote in #note-22:
> > As far as I understand rightward assignment (I’m not currently using Ruby 3), that’s not something that is legal.
> 
> Of course it's not currently legal to use rightward assignment in the method signature, but I think if you compare with positional arguments it's easy to see the similarity:
> `def foo(name = 'Ciri' => node_name)`
> Would be pretty much equivalent to the currently valid:
> `name = 'Ciri' => node_name`
> And I think it's not much of a stretch to go from `name='Ciri' => node_name` to `name:'Ciri' => node_name`, at least for the method signature.
> 
> Now if only `name = 'Ciri' => @node_name` was legal (#18408) it would also make sense to use it in the method signature.

The ship has sailed on rightward assignment (I think it’s a mistake and unforgivably ugly, I don’t understand the use case at all, and I suspect that I will never use it), but my comment was specifically about `=> node_name`, which is the case for `name: => node_name`.

> austin (Austin Ziegler) wrote in #note-24:
> > `def name(for: { "a" => 0, "b" => 1 } => for_target, bar: => bar_target)`
> 
> You have to admit that example is a bit contrived. I've never seen such a hash used as a default value. :-)
> But really I think everyone understands that the parameters in the method signature have slightly different semantics that the same syntax elsewhere. Depending on the presence of `def`, `foo(bar=42)` is a default value, not an assignment. `foo(bar:)` is a required keyword argument, not a "hash value omission". Etc.

I have used a populated hash as a default value. I haven’t done so frequently, but there are cases where it makes sense.

----------------------------------------
Feature #15192: Introduce a new "shortcut assigning" syntax to convenient setup instance variables
https://bugs.ruby-lang.org/issues/15192#change-95352

* Author: jjyr (Jinyang Jiang)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
----------------------------------------
Motivation:

Introduce a new syntax for convenient setup instance variables for objects.

The problem:

Currently, setup instance variables in Ruby is too verbose. 
Basically, we need to write the meaningless assigning code again and again to assign variables

``` ruby
class Person
  def initialize(name:, age:, gender:, country:)
    @name = name
    @age = age
    @gender = gender
    @country = country
  end
end


# we can use Struct to avoiding this

Person = Struct.new(:name, :age, :gender, :country, keyword_init: true)

# let's see a real-world case, which can't use Struct to describe an initializing process, from https://github.com/ciri-ethereum/ciri/blob/748985ccf7a620a2e480706a5a6b38f56409d487/lib/ciri/devp2p/server.rb#L54
# Because we want to do something more than just assigning instance variables

class Server
      def initialize(private_key:, protocol_manage:, bootstrap_nodes: [],
                     node_name: 'Ciri', tcp_host: '127.0.0.1', tcp_port: 33033)
        @private_key = private_key
        @node_name = node_name
        @bootstrap_nodes = bootstrap_nodes
        @protocol_manage = protocol_manage
        server_node_id = NodeID.new(@private_key)
        caps = [Cap.new(name: 'eth', version: 63)]
        @handshake = ProtocolHandshake.new(version: BASE_PROTOCOL_VERSION, name: @node_name, id: server_node_id.id, caps: caps)
        @tcp_host = tcp_host
        @tcp_port = tcp_port
        @dial = Dial.new(bootstrap_nodes: bootstrap_nodes, private_key: private_key, handshake: @handshake)
        @network_state = NetworkState.new(protocol_manage)
        @dial_scheduler = DialScheduler.new(@network_state, @dial)
      end
end


# Introduce a new "shortcut assigning" syntax for convenient setup

class Person
  # use @ prefix to describe instance variables.
  def initialize(@name:, @age:, @gender:, @country:)
  end

  # equal to
  def initialize2(name:, age:, gender:, country:)
    @name = name
    @age = age
    @gender = gender
    @country = country
  end

  # it should also work on position style arguments
  def initialize2(@name, @age, @gender, @country)
  end
end

# Our real-world case can be rewritten as below
class Server
      def initialize(@private_key:, @protocol_manage:, @bootstrap_nodes: [],
                     @node_name: 'Ciri', @tcp_host: '127.0.0.1', @tcp_port: 33033)
        server_node_id = NodeID.new(@private_key)
        caps = [Cap.new(name: 'eth', version: 63)]
        @handshake = ProtocolHandshake.new(version: BASE_PROTOCOL_VERSION, name: @node_name, id: server_node_id.id, caps: caps)
        @dial = Dial.new(bootstrap_nodes: @bootstrap_nodes, private_key: @private_key, handshake: @handshake)
        @network_state = NetworkState.new(@protocol_manage)
        @dial_scheduler = DialScheduler.new(@network_state, @dial)
      end
end

# consider to keep consistency, this "shortcut assigning" syntax should work for non-initialize methods
class Foo
  def bar(@still_works)
    p @still_works
  end
end
```



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