how to wrap method of singleton class

[Ittay Dror]

Hi,


Given a class:

class Foo

class << self

def foo

puts 'foo'

end

end

end


How do I write a module, so that when included in Foo it will wrap the
method foo so that Foo.foo will print:

bar

foo


?


Thank you

Ittay

 

[James Coglan]

[Note: parts of this message were removed to make it a legal post.]

How do I write a module, so that when included in Foo it will wrap the
method foo so that Foo.foo will print:

You can't (at least not without doing some sneaky metaprogramming -- this
code is still a work in progress: http://gist.github.com/25104). A class's
own methods take precedence over any modules mixed into it. What you can do
is reopen the singleton class and store a reference to the old method:

class << Foo # Foo singleton class
old_foo = Foo.methodfoo)
define_methodfoo) do |*args|
old_result = old_foo.call(*args)
old_result.upcase
end
end

Foo.foo #=> "FOO"

You must use define_method for this instead of def. def does not use a block
so you won't get a closure, which you need to retain visibility of the
old_foo variable.

 

[Ittay Dror]

[Note: parts of this message were removed to make it a legal post.]

You can't (at least not without doing some sneaky metaprogramming -- this
code is still a work in progress: http://gist.github.com/25104). A class's
own methods take precedence over any modules mixed into it. What you can do
is reopen the singleton class and store a reference to the old method:

class << Foo # Foo singleton class
old_foo = Foo.methodfoo)
define_methodfoo) do |*args|
old_result = old_foo.call(*args)
old_result.upcase
end
end

doing it this way, i can do:
class << Foo
alias_method riginal, :foo
def foo
puts 'bar'
original
end
end

but i want a module i can mix in. (for regular methods, the module can
use the included callback to alias the methods, just not sure how to do
that for a singleton class)