From: "bkuhlmann (Brooke Kuhlmann) via ruby-core" <ruby-core@...>
Date: 2023-01-04T16:48:29+00:00
Subject: [ruby-core:111627] [Ruby master Feature#8088] Method#parameters (and friends) should provide useful information about core methods

Issue #8088 has been updated by bkuhlmann (Brooke Kuhlmann).





I've been bitten by this same issue (see #19301) in Ruby 3.2.0 with the introduction of the new [Data](https://www.alchemists.io/articles/ruby_data) class. At the time of opening that issue, I didn't fully realize how *untruthful* `Method#parameters` is with C-based implementations since it answers `[[rest]]` for parameters which is incorrect and *very hard* to *dynamically* build the *correct* argument list when given wrong parameters. In case it helps, here's a code snippet that demonstrates the issue when using only `Data` and `Struct` objects:



``` ruby

DataExample = Data.define :one, :two

StructAny = Struct.new :one, :two

StructKeywordOnly = Struct.new :one, :two, keyword_init: true



models = [DataExample, StructAny, StructKeywordOnly]

arguments = [{one: 1, two: 2}]



models.each do |model|

  puts "#{model}#initialize parameters: #{model.method(:initialize).parameters}"

end



puts



models.each do |model|

  print "#{model}: "

  puts model[*arguments]

rescue ArgumentError => error

  puts error.message

end



# DataExample#initialize parameters: [[:rest]]

# StructAny#initialize parameters: [[:rest]]

# StructKeywordOnly#initialize parameters: [[:rest]]

#

# DataExample: missing keyword: :two

# StructAny: #<struct StructAny one={:one=>1, :two=>2}, two=nil>

# StructKeywordOnly: #<struct StructKeywordOnly one=1, two=2>

```



In all three models, messaging `model.method(:initialize).parameters` will always answer `[[rest]]` for parameters so when I build my arguments (i.e. `[{one: 1, two: 2}]`) in the same format as dictated from the `Method#parameters` then the only model that gives me the correct instance is the `StructKeywordOnly` model because using `keyword_init: true` does that coercion for me. ����



My C knowledge is pretty terrible so I don't know how hard this would be to fix but would definitely welcome having accurate and truthful `Method#parameters` information for C-based implementations.



----------------------------------------

Feature #8088: Method#parameters (and friends) should provide useful information about core methods

https://bugs.ruby-lang.org/issues/8088#change-100998



* Author: headius (Charles Nutter)

* Status: Open

* Priority: Normal

----------------------------------------

I was wiring up #parameters to work for native methods today when I realized MRI doesn't give very good information about variable-arity native methods:



ext-jruby-local ~/projects/jruby $ ruby2.0.0 -e "p ''.method(:gsub).to_proc.parameters"

[[:rest]]



ext-jruby-local ~/projects/jruby $ jruby -e "p ''.method(:gsub).to_proc.parameters"

[[:req], [:opt]]



I think MRI should present the same as JRuby here; gsub is obviously not a rest-arg method and you can't call it with less than 1 or more than 2 arguments. JRuby's presenting the right output here.



I'm probably going to have to change JRuby to do the less-helpful version so we're compliant and tests pass, but I think the specification of #parameters should be that it presents the JRuby version about rather than the MRI version.







-- 

https://bugs.ruby-lang.org/

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