Feature #440: Better introspection for methods (declaring class, arity)

• Status: Closed
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[lkoskela (Lasse Koskela)]

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Tools relying on introspection would benefit from having access to information such as:

1. where was a given method declared, and
2. how many arguments does a method accept.

Currently, for 1) one needs to parse the output of Object.new.method(:name).to_s to resolve where a method was inherited from.
For 2), one can only get the number of required arguments with Object.new.method(:name).arity, which isn't sufficient if you want to use the optional arguments, too. With the current implementation of arity, one needs to just "assume" that one can throw an arbitrary number of arguments at the method and see if it fails.

The use case for these enhancements is coming from the open source Robot Framework (http://www.robotframework.org). It's a testing harness where you plug in implementations of test cases in the form of "keyword libraries" implemented in Python, Java, or (hopefully soon) Ruby. In order to report available "keywords" (actions available for the test author, implemented as public methods) to the user, the framework needs to scan available keyword libraries for suitable methods and determine how many arguments each keyword accepts (ideally, with the names of those arguments). Improving Ruby's introspection capabilities would be a boost for Ruby's viability as a Robot Framework keyword library implementation language.

1. would seem like a simple thing to do, given that the information is already available for Method#to_s. I'm not proficient with C, but I might be able to implement that myself as a patch if someone could point me to the right direction regarding the location in the source files.
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[ko1 (Koichi Sasada)]

• Assignee set to matz (Yukihiro Matsumoto)

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[ko1 (Koichi Sasada)]

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Current trunk seems to support your requirements. Could you confirm about this issue?
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[lkoskela (Lasse Koskela)]

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The first aspect of the issue has been improved via the "source_location" and "receiver" methods being available on the Method object.

It seems to me that the arity stuff, however, is the same as with the 1.8.x branch? That is, aspect 2) of this issue is still current.
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[rogerdpack (Roger Pack)]

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if you don't mind a hack then
RubyVM::InstructionSequence.disasm
might help.
Looks like it would be nice to add something to do this, though, since it seems difficult to tell from the #arity call to see how many optional and non optional arguments there are.
Cheers.
-=R
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[rogerdpack (Roger Pack)]

• Status changed from Open to Feedback

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Has this been addressed with the methopara gem and/or http://github.com/maca/arguments
?
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[mame (Yusuke Endoh)]

• Status changed from Feedback to Closed

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Hi,

Tools relying on introspection would benefit from having access to information such as:

1. where was a given method declared, and
2. how many arguments does a method accept.

I think the requests has already been solved by Method#source_location
and Method#parameters respectively. So I close this ticket.

--
Yusuke Endoh [e-mail]
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