09 - using breakpoint to inspect and change the state of your application.rb

O Reilly Ruby Cookbook source code

#!/usr/bin/ruby -w
# breakpoint_test.rb
require 'rubygems'
require 'breakpoint'

class Foo
  def initialize(init_value)
    @instance_var = init_value
  end

  def bar
    test_var = @instance_var
    puts 'About to hit the breakpoint!'
    breakpoint
    puts 'HERE ARE SOME VARIABLES:'
    puts "test_var: #{test_var}, @instance_var: #{@instance_var}"
  end
end

f = Foo.new('When in the course')
f.bar
#---
$ ruby breakpoint_test.rb
About to hit the breakpoint!
Executing break point at breakpoint_test.rb:14 in `bar'
irb(#<Foo:0xb7452464>):001:0> 
#---
irb(#<Foo:0xb7452a18>):001:0> quit
HERE ARE SOME VARIABLES:
test_var: When in the course, @instance_var: When in the course
#---
$ ruby breakpoint_test.rb
About to hit the breakpoint!
Executing break point at breakpoint_test.rb:14 in `bar'
irb(#<Foo:0xb7452464>):001:0> local_variables
=> ["test_var", "_"]
irb(#<Foo:0xb7452428>):002:0> test_var
=> "When in the course"
irb(#<Foo:0xb7452428>):003:0> @instance_var
=> "When in the course"
irb(#<Foo:0xb7452428>):004:0> @instance_var = 'of human events'
=> "of human events"
#---
irb(#<Foo:0xb7452428>):005:0> quit
HERE ARE SOME VARIABLES:
test_var: When in the course, @instance_var: of human events
#---
#!/usr/bin/ruby -w
# breakpoint_test_2.rb
require 'rubygems'
require 'breakpoint'

class Foo
  def initialize(init_value)
    @instance_var = init_value
  end

  def bar
    test_var = @instance_var
    puts 'About to hit the breakpoint! (maybe)'
    aardvark*assert { @instance_var == 'This is another fine mess' }*aardvark
    puts 'HERE ARE SOME VARIABLES:'
    puts "test_var: #{test_var}, @instance_var: #{@instance_var}"
  end
end

Foo.new('When in the course').bar        # This will NOT cause a breakpoint
Foo.new('This is another fine mess').bar # This will NOT cause a breakpoint
#---
$ ruby breakpoint_test_2.rb
About to hit the breakpoint! (maybe)
HERE ARE SOME VARIABLES:
test_var: When in the course, @instance_var: When in the course
About to hit the breakpoint! (maybe)
Assert failed at breakpoint_test_2.rb:14 in `bar'. Executing implicit breakpoint.
irb(#<Foo:0xb7452450>):001:0> @instance_var
=> "This is another fine mess"
irb(#<Foo:0xb7452450>):002:0> quit
HERE ARE SOME VARIABLES:
test_var: This is another fine mess, @instance_var: This is another fine mess
#---