Overriding a class method

Here’s a quick question for the Meta-programming gurus

start with

class A
def self.method_a
puts “A”
end
end

How would I override method_a in such a way that the original method_a
could be called at the end? sort of like that way you can call ‘super’
from a subclass.

_Kevin

super still works:

irb(main):001:0> class A
irb(main):002:1> def self.method_a
irb(main):003:2> puts “A”
irb(main):004:2> end
irb(main):005:1> end
=> nil
irb(main):006:0> class NewA < A
irb(main):007:1> def self.method_a
irb(main):008:2> puts “NewA”
irb(main):009:2> super
irb(main):010:2> end
irb(main):011:1> end
=> nil
irb(main):012:0> NewA.method_a
NewA
A

Farrel

I’m not a guru, but the following works for me, though it is not very
elegant:

class A
def self.method_a
puts “A”
end
end

class A
@@old_method_a = self.method(:method_a)
def self.method_a
puts “B”
@@old_method_a.call
end
end

A.method_a # outputs “B”, then “A”

  • Jake McArthur

Oh wait I think I misunderstood the question are you looking to
overwrite it in the same
class?

Yeah, not looking to subclass.

On Thursday, April 20, 2006, at 3:59 AM, Farrel L. wrote:

Oh wait I think I misunderstood the question are you looking to
overwrite it in the same
class?

_Kevin

On 4/19/06, Kevin O. [email protected] wrote:

Yeah, not looking to subclass.

class A
def self.meth_a
puts “one”
end
end

class A
class << self; alias meth_a_old meth_a end
def self.meth_a
meth_a_old
puts “two”
end
end

Though I personally think use of alias for this sort of thing as a
“hack” (just my opinion of course). Another technique is to use a
lexical closure:

class A
def self.meth_a
puts “one”
end
end

class A
old_a = method(:meth_a)

The ugly part. This usually is nicer for instance methods.

You could write this a few different ways but they are all

ugly. Possibly something to factor out as a method.

sclass = class << self; self end
sclass.send :define_method, :meth_a do
old_a.call
puts “two”
end
end

Both are messy but one is less likely to collide or cause problems
with other code (not to mention littering the class with aliases).

Brian.

Thanks!

I am slowly but surely getting the hang of this metaprogramming thing.

On Thursday, April 20, 2006, at 4:49 AM, Brian M. wrote:

class << self; alias meth_a_old meth_a end
class A
sclass = class << self; self end

_Kevin

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