[ruby-core:95570] [Ruby master Feature#14145] Proposal: Better Method#inspect

[zverok.offline@gmail.com]

Issue #14145 has been updated by zverok (Victor Shepelev).


This PR provides method parameters inspect: https://github.com/ruby/ruby/pull/2618
Implementation is most probably not optimal (to say the least), I am ready to fix it by comments. At least the tests and implementation should handle all possible cases.

Examples:

```ruby
def m(a, b=nil, *c, d:, e: nil, **rest, &block)
end

p method(:m)
#=> #<Method: m(a, b=<default>, *c, d:, e: <default>, **rest, &block) ...>

# Internal classes with param names not known:
p Array.instance_method(:slice)
#=> #<UnboundMethod: Array#slice(*)>
p Array.instance_method(:grep)
#=> #<UnboundMethod: Array(Enumerable)#grep(arg1)>
```

----------------------------------------
Feature #14145: Proposal: Better Method#inspect
https://bugs.ruby-lang.org/issues/14145#change-82351

* Author: zverok (Victor Shepelev)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
The idea: When investigating (in example scripts, debugger or console) the library you are unfamiliar with, Ruby's reflection is very useful mechanism to understand "what it can": classes, modules, their constants, methods and so on.
I propose to expose a bit more information Ruby has internally in `Method#inspect`:


```ruby
# before:
some_interesting_object.method(:foo) # => #<Method Klass#foo>
# after:
some_interesting_object.method(:foo) # => #<Method Klass#foo(first_arg, *other_args, keyword_arg:)>
```

Dead-naive implementation:

```ruby
class Method
  def signature
    recv = case receiver
    when Module
      "#{receiver.name}."
    else
      "#{receiver.class}#"
    end
    parameters.map.with_index { |(type, name), i|
      case type
      when :req then "#{name || "param#{i+1}"}"
      when :opt then "#{name || "param#{i+1}"} = <default>"
      when :keyreq then "#{name || "kw#{i+1}"}:"
      when :key then "#{name || "kwparam#{i+1}"}: <default>"
      when :rest then "*#{name || "rest"}"
      when :keyrest then "**#{name || "kwrest"}"
      end
    }.join(', ').prepend("#{recv}#{name}(") << ")"
  end

  def inspect
    "#<#{self.class.name} #{signature}>"
  end
end

```

This works "sub-optimal" for methods implemented in C, yet pretty decently for Ruby-implemented methods:

```ruby
# C method, default param names
[1,2,3].method(:at)
# => #<Method Array#at(param1)>

# Ruby method, proper param names
CGI.method(:escape)
# => #<Method CGI.escape(string)>
Addressable::URI.method(:parse)
# => #<Method Addressable::URI.parse(uri)>
Addressable::URI.method(:join)
 => #<Method Addressable::URI.join(*uris)>

# We can't extract default values, but at least we can say they are there
Addressable::URI.method(:heuristic_parse)
# => #<Method Addressable::URI.heuristic_parse(uri, hints = <default>)>
```

If the proposal is accepted, I am ready to implement it properly in C (for all callable objects: `Method`, `UnboundMethod`, `Proc`)



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