[ruby-core:55979] [ruby-trunk - Feature #8629] Method#parameters should include the default value

Issue #8629 has been updated by headius (Charles Nutter).


I could see this being valid if it were limited to showing literal types when the default value is a literal and something like :expression when it's anything more complex (though that obviously isn't the right choice since :expression as a default value is a perfectly-value literal.

For non-literals (and by literals I mean values that could safely be evaluated outside the context of that method... strings, symbols, floats, fixnums, bignums, true/false/nil) there's no real way to determine the type since it will depend on a method call, a constant lookup, or in the case of arrays and hashes, the elements contained within.

It would also not be possible to know whether the default value could safely be evaluated if it contained *any* constant lookups or method calls, since they may require being within the activation of that method (scoping, self methods, etc).
----------------------------------------
Feature #8629: Method#parameters should include the default value
https://bugs.ruby-lang.org/issues/8629#change-40476

Author: rosenfeld (Rodrigo Rosenfeld Rosas)
Status: Open
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: 


def a_method arg1=1, now = Time.now, arg2 = arg1 + 1
end

method(:a_method).parameters == [[:opt, :arg1], [:opt, :now], [:opt, :arg2]]

I'd prefer if it could return [[:opt, :arg1, 1], [:opt, :now, now_proc], [:opt, :arg2, arg2_proc]], and expect now_proc[] to be the current time and arg2_proc[] to raise an exception since arg1 is not defined.

Rationale:

Ruby doesn't support optional typing such as:

def a_method Date date, Integer n = 0, String name = ''
end

Groovy does, and this allows Grails to perform some interesting stuff, like params binding in controller methods.

If Ruby allowed the default values to be introspected, web frameworks would be able to achieve a similar binding feature. For example, they could use the default to decide upon how to bind the param. They could use the default_value.class or if the default value is nil it could be specified by providing the class itself. For instance:

def an_action name: '', parent_name: String, age: Integer, date: Date.today
end

Of course, you'd need to set up the framework so that it knows how you intend parse dates and other special types from string, but this could make the developer life easier and safer against this kind of attack (like trying to instantiate a hash, etc).

An alternative would be something like:

def an_action params = {name: :string, age: :integer, date: :date}
end

You get the idea. Many APIs would be possible to be built if we're able to easily get access to the default values when inspecting a method.

Could you please consider this idea?


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