removing methods (motm 2010.01)
TRANSCRIPT
Removing MethodsRuby Method of the MonthKevin Munc => @muncman
Adding a Method
class String def ruby_rocks? true #dat endend
Fancy New Method
"rails".ruby_rocks?=> true
Remove It!class String remove_method :ruby_rocks?end
Remove It!class String remove_method :ruby_rocks?end"rails".ruby_rocks?NoMethodError: undefined method `ruby_rocks?' for "rails":String
A Redefined Method
class Crb def to_s "Thanks Randall!" endend
Redefinition in Action
columbusrb = Crb.new
Redefinition in Action
columbusrb = Crb.new
columbusrb.to_s
Redefinition in Action
columbusrb = Crb.new
columbusrb.to_s=> "Thanks Randall!"
Redefinition Removalclass Crb remove_method :to_send
Note that we didn’t have to get a new instance for the removal to take effect.
Redefinition Removalclass Crb remove_method :to_send
Note that we didn’t have to get a new instance for the removal to take effect.
columbusrb.to_s
Redefinition Removalclass Crb remove_method :to_send
Note that we didn’t have to get a new instance for the removal to take effect.
columbusrb.to_s=> "#<Crb:0x101651538>"
Inherited Methodror = “Ruby on Rails”ror.to_s=> "Ruby on Rails"
We get the to_s from Object.
Note that the removal takes effect for instances already declared.
Inherited Methodror = “Ruby on Rails”ror.to_s=> "Ruby on Rails"
We get the to_s from Object.
Note that the removal takes effect for instances already declared.
class String remove_method :to_send
Inherited Methodror = “Ruby on Rails”ror.to_s=> "Ruby on Rails"
We get the to_s from Object.
Note that the removal takes effect for instances already declared.
class String remove_method :to_sendror.to_s=> "#<String:0x101682b88>"
Removal Locationclass Object remove_method :to_send
Defined in Kernel.
Object mixes in Kernel.
Removal Locationclass Object remove_method :to_send
Defined in Kernel.
Object mixes in Kernel.
NameError: method `to_s' not defined in Object
Put It All Back
class Crb def to_s "Thanks Randall!" endend
Starting from a clean slate, so String still has to_s, etc.
Undefine the Redefine Different than removal!
class Crb undef_method :to_send
Interesting that the default output of to_s is present in the output.
Undefine the Redefine Different than removal!
class Crb undef_method :to_send
Interesting that the default output of to_s is present in the output.
columbusrb.to_s
Undefine the Redefine Different than removal!
class Crb undef_method :to_send
Interesting that the default output of to_s is present in the output.
columbusrb.to_sNoMethodError: undefined method `to_s' for #<Crb:0x101651538>
Definitely Undefinedclass String undef_method :to_send
Note that the undef also applied to subclasses of the type where the undef happened.
Definitely Undefinedclass String undef_method :to_send
"rails".to_sNoMethodError: undefined method `to_s' for "rails":String
Note that the undef also applied to subclasses of the type where the undef happened.
Defined Elsewhereclass Crb undef_method :object_idend
The undef succeeds because the method is available to class Crb.
Defined Elsewhereclass Crb undef_method :object_idend
columbusrb = Crb.newcolumbusrb.object_idNoMethodError: undefined method `object_id' for #<Crb:0x10166d7d8>
The undef succeeds because the method is available to class Crb.
Method Removalremove_method :symbol
Removed from the specific type only.
Ruby still searches up the hierarchy.
undef_method :symbolPrevents calls to the method regardless of the type’s hierarchy.
Both defined in the Module class.
Finer Points(pun intended)
You can call remove_method only on a method actually defined within the class itself.
You can call undef_method on a method accessible from the class (inherited or mixed in).
Questions?Photo Credits:
http://www.flickr.com/photos/tomscott/4225623/http://www.flickr.com/photos/slayer23/2215384832/
http://www.flickr.com/photos/andreweason/268627274/http://www.flickr.com/photos/tomscott/28188883/http://www.flickr.com/photos/jonmikel/259535350/