cheap_advice.slides.textile

!SLIDE
!TITLE Cheap Advice

Cheap Advice

• Kurt Stephens
• Enova Financial — http://enovafinancial.com
• 2011/11/14
• Slides — http://kurtstephens.com/pub/cheap_advice.slides/index.html
• Code — http://github.com/kstephens/cheap_advice

!SLIDE
!TITLE Clean Code

Clean Code

@ ruby

class MyClass
def foo; 42; end
end
class MyOtherClass
def bar; 43; end
end
a = MyClass.new
b = MyOtherClass.new
a.foo
b.bar

@

!SLIDE
!TITLE Add Logging

Add Logging

@ ruby

class MyClass
def foo
$stderr.puts “#{self}#foo => 42”
42
end
end
class MyOtherClass
def bar
$stderr.puts “#{self}#bar => 43”
43
end
end
a = MyClass.new
b = MyOtherClass.new
a.foo
b.bar

@

!SLIDE
!TITLE Add Security

Add Security

@ ruby

class MyClass
def foo
raise “SecurityError” unless $roles.include?(“MyClass#foo”)
$stderr.puts “#{self}#foo => 42”
42
end
end
class MyOtherClass
def bar
raise “SecurityError” unless $roles.include?(“MyClass#bar”)
$stderr.puts “#{self}#bar => 43”
43
end
end
a = MyClass.new
b = MyOtherClass.new
$roles = [ “MyClass#foo” ]
a.foo
b.bar

@

!SLIDE
!TITLE YUCK!

…YUCK!

@ ruby

class MyClass
def foo

1. YUCK!: raise “SecurityError” unless $roles.include?(“MyClass#foo”)
2. YUCK!: $stderr.puts “#{self}#foo => 42”
   42
   end
   end
   class MyOtherClass
   def bar
3. YUCK!: raise “SecurityError” unless $roles.include?(“MyClass#bar”)
4. YUCK!: $stderr.puts “#{self}#bar => 43”
   43
   end
   end
   a = MyClass.new
   b = MyOtherClass.new
   $roles = [ “MyClass#foo” ] # ???
   a.foo
   b.bar

@

!SLIDE
!TITLE Dumb and Clean, Smart and Dirty

Dumb and Clean, Smart and Dirty

• Real World is Smart Code.
• Dumb Code is Clean, Smart Code is Dirty.
• Get Dirt Out Of Code — (problem-domain vs. solution-domain)
• Sweep It Somewhere Else — (modularize the smart dirt)
• Don’t be Dirty All the Time — (dynamic, stateful dirt: logging, debugging, security, etc.)

!SLIDE
!TITLE Separation of Concerns

Separation of Concerns

• Logging
• Security

… are not problem-domain issues.

!SLIDE
!TITLE Advice

Advice

• Commonplace in the Lisp world, (esp. Emacs).
• Advice is function that wraps another function: “before”, “after” or “around”.
• Advice can be added or removed at run-time.

!SLIDE
!TITLE Advice != Aspects

Advice != Aspects

• Aspects are woven into code based on complex “codepoint” criteria at build-time (or load-time).
• Advice is applied to a more well-known constructs: applicable objects: functions, methods, etc.
• Advice are objects.
• Advice can be added and removed at run-time.

!SLIDE
!TITLE Cheap Advice

Cheap Advice

• … adds dynamic Advice to Ruby methods.
• … is applied to methods.
• … are stateful objects.
• … can be added and removed at run-time.
• … are configurable.

!SLIDE
!TITLE Logging Advice

Logging Advice

@ ruby

1. Advice
   trace_advice = CheapAdvice.new(:around) do | ar, body |
   ar.advice[:log] <<
   "#{Time.now.iso8601(6)} " <<
   “#{ar.rcvr.class} #{ar.meth} #{ar.rcvr.object_id}\n”
   body.call
   ar.advice[:log] <<
   "#{Time.now.iso8601(6)} " <<
   "#{ar.rcvr.class} #{ar.meth} #{ar.rcvr.object_id} " <<
   “=> #{ar.result.inspect}\n”
   end
2. State attached to trace_advice.
   trace_advice[:log] = File.open(“trace.log”, “a+”)

@

!SLIDE
!TITLE Applying Advice

Applying Advice

@ ruby

…

1. Activate trace_advice:
   trace_advice.advise!(MyClass, :foo)
   trace_advice.advise!(MyOtherClass, :bar)
   a.foo
   b.bar

1. Disable trace_advice:
   trace_advice.disable!
   a.foo
   b.bar
   @

!SLIDE
!TITLE Configuration

Configuration

@ yaml

:advice:
~:
:enabled: false
:options:
:trace:
:logger:
:name: :default

‘MyClass’: :advice: trace ‘MyClass#foo’: :enabled: false ‘MyClass#bar’: :enabled: false

@

!SLIDE
!TITLE Security Advice

Security Advice

You get the idea.

!SLIDE
!TITLE Example

See example/ex01.rb

!SLIDE
!TITLE CheapAdvice

Questions?

Code!

• http://github.com/kstephens/cheap_advice
• gem install cheap_advice