Use `source_location` to find where a method is defined

ruby_introspection.md

TL;DR

Use ruby's Method#source_location to determine where a method is defined.

method(:s).source_location
# => ["..snip../gems/sexp_processor-4.2.1/lib/sexp.rb", 332]

Who defined s?

I've been using flog to get some simple code-quality metrics. I happily added it to my Gemfile's development group. Later, I wrote something like

t = 'foo' + s

and I wasn't defining s, so I expected NameError or NoMethodError. Instead,

TypeError: can't convert Sexp into String

Surprising. So, where is the s method defined? Happily, ruby knows. First, instantiate the s method.

# send the `method` message to the same reciever (in this case,
# implicit) that we sent the `s` message to.
method(:s)
# => #<Method: Object#s>

OK, s is an instance method on Object. Cool, but who defined s?

method(:s).source_location
# => ["..snip../gems/sexp_processor-4.2.1/lib/sexp.rb", 332]

Awesome, it's defined on sexp.rb, line 332. It turns out sexp_processor is a dependency of flog.

Defining a method with as common a name as s on Object is a bit too much pollution for my taste, seeing as my code doesn't use s. So, I've removed flog from my bundle, though I still use the gem often.

Object as an Implicit Receiver

In the above example, why is Object the implicit receiver?

On the top level, a special instance of Object named "main" is the self. ("Three implicit contexts in Ruby", Yuki Sonoda)

This is easy to see in irb:

self
# => main
self.class
# => Object

Followup Thoughts

1. How well does source_location (docs) work for methods defined with Module#define_method (docs)?