Ruby debugging: How to find out which method or variable is responding?

Question

When debugging ruby code with some complexity, it is easy to get confused by stacked method definitions, and by naming conflicts with local variables.

I am looking for a fast way to find out which method or variable responds to an expression, something like any_expression.identify.

The best I could find so far is:

method(:happy)
#=> #<Method: Object(Helper)#happy>

method(:happy).source_location
#=> ["/home/somebody/project/lib/helper.rb", 9]

Unfortunately a local variable (like happy=42) will precede, but method(:happy) will still return the other method.

Any ideas?

Answer 1

You don't have to prefix with self.class.new. It wouldn't work if the class doesn't have constructor with no arguments anyway.

local_variables.include?(:foo) # local variable
method(:foo)                   # method

---

Another alternative is to use the defined? keyword:

foo = 42
def bar; end

defined?(foo) # => "local-variable"
defined?(bar) # => "method"

---

In pry, you can use show-method:

show-method bar # =>
  # From: (pry) @ line 104:
  # Owner: Object
  # Visibility: public
  # Number of lines: 1

  # def bar; end

And ls:

ls foo # =>
  # Comparable#methods: between?
  # Numeric#methods: 
  #   +@      conj       imaginary     pretty_print_cycle  rectangular           
  #   abs2    conjugate  nonzero?      quo                 remainder             
  #   angle   eql?       phase         real                singleton_method_added
  #   arg     i          polar         real?               step                  
  #   coerce  imag       pretty_print  rect                to_c                  
  # Integer#methods: 
  #   ceil         downto  gcdlcm    next       pred         times   to_r    
  #   chr          floor   integer?  numerator  rationalize  to_i    truncate
  #   denominator  gcd     lcm       ord        round        to_int  upto    
  # Fixnum#methods: 
  #   %  **  -@  <<   ==   >=  ^           div     fdiv       modulo  succ  zero?
  #   &  +   /   <=   ===  >>  abs         divmod  inspect    odd?    to_f  |    
  #   *  -   <   <=>  >    []  bit_length  even?   magnitude  size    to_s  ~

---

I don't think there is a way to check exactly where a local variable was defined. However, you could always reverse search in your console to see the line that defined it:

Ctrl + r: foo = => (reverse-i-search)`foo =': foo = 42