From: bradley.t.herman@...
Date: 2018-10-15T17:36:21+00:00
Subject: [ruby-core:89408] [Ruby trunk Feature#15049] [Request] Easily access all keyword arguments within a method

Issue #15049 has been updated by bherms (Bradley Herman).


duerst (Martin D��rst) wrote:
> Maybe I'm totally confused, but what's wrong with using **keyword_arguments?

I agree with zverok's answer.

The main reason for not just doing **args is that you lose several of the benefits of using keyword arguments in the first place: 1) lowering connascence , 2) enforcing requirements (required kargs), 3) settings defaults.

~~~ ruby
def post(required:, other_required:, defaulted: 'default')
end

def post(**kargs)
  raise ArgumentError, 'missing keyword "required"' unless kargs.has_key?(:required)
  raise ArgumentError, 'missing keyword "other_required"' unless kargs.has_key?(:other_required)
  kargs.reverse_merge!(defaulted: 'default')
end
~~~

Those two method definitions are *very* different IMO and the first is far superior.  Obviously we could DRY up the required argument checks, but it still wouldn't be ideal.

----------------------------------------
Feature #15049: [Request] Easily access all keyword arguments within a method
https://bugs.ruby-lang.org/issues/15049#change-74448

* Author: bherms (Bradley Herman)
* Status: Feedback
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
As a developer, I'd like to leverage the power of keyword arguments (requirements, defaults, etc) and then be able to access a hash of all the arguments supplied.

~~~ ruby
def foo(bar:, baz: 1, qux: 2...)
  post('/', body: kargs)
end
~~~

This is currently possible by leveraging the RubyVM debug inspector and some meta programming to retrieve the binding and name of the calling method.  There is a gem https://github.com/banister/binding_of_caller that abstracts away the logic of crawling through the frame bindings in the debug inspector to find the binding of the caller, but I feel like this functionality would be useful in Ruby.

With the binding_of_caller gem, you can hack together a kargs method like so:

~~~ ruby
def kargs
  method(caller_locations(1,1)[0].label).parameters.map do |(_type, name)|
    [name, binding.of_caller(2).local_variable_get(name)]
  end.to_h
end
~~~

This gets the name of the calling method, pulls the local variables from the method, retrieves the binding, and then retrieves the variables from the binding.  By exposing a simpler API to retrieve the caller binding, a `kargs` method could be added to Ruby fairly easily I would think.





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