A method to trace variable changes in your project. Set `__trace_if__` to return true to print *every* line, or have it print conditionally. In the example below I print only when the variable `boof` changes.

ruby_trace.rb

lambda do
  trace_default_frame = lambda do
    { locals: {} }
  end

  trace_stack = [trace_default_frame[]]

  set_trace_func proc { |event, file, line, id, binding, classname|
    if event == 'call' || event == 'c-call'
      trace_stack << trace_default_frame[]
    elsif event == 'return' || event == 'c-return'
      trace_stack.pop
      trace_stack << trace_default_frame[] if trace_stack.empty?
    end

    binding.eval('local_variables').each do |variable_sym|
      # don't include local variables used within this lambda
      next if [:trace_default_frame, :trace_stack].include?(variable_sym)

      old = trace_stack.last[:locals][variable_sym]
      new = binding.eval(variable_sym.to_s)

      begin
        original = new.dup
        binding.eval("lambda { |v| #{variable_sym} = v}")[new.dup]
      rescue
        original = new
      end
      trace_stack.last[:locals][variable_sym] = original

      unless old.nil? || old == new
        #binding.eval("lambda { |v| #{variable_sym} = v }")[old]
        if Kernel.__trace_if__(event, file, line, id, binding, classname, variable_sym)
          printf "%s:%-2d %s changed from '%s' to '%s'\n", file, line, variable_sym, old, new
        end
      end
    end
  }
end.call

module Kernel
  class << self
    def __trace_if__(event, file, line, id, binding, classname, variable_sym)
      variable_sym == :boof
    end
  end
end

boof = 1

10.times do |i|
  boof += 1
end