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comp.lang.ruby

best praxis to wrap methods?

Meinrad Recheis

3/7/2006 9:40:00 AM

hello fellow rubyists,

is there an elegant way to define a singleton method from a given symbol
without using eval? what i am doing is this:

def make_wrapper object, method
eval %{
def object.#{method}
# do something here
super # call the wrapped method
end
}
end

# example of usage:
make_wrapper STDOUT, :puts

using eval works, but it seems not to be the best solution. is there
annother way do define methods from a given symbol?

-- henon
3 Answers

Meinrad Recheis

3/7/2006 9:43:00 AM

0

On 3/7/06, Meinrad Recheis <meinrad.recheis@gmail.com> wrote:
>
> hello fellow rubyists,
>
> is there an elegant way to define a singleton method from a given symbol
> without using eval? what i am doing is this:
>
> def make_wrapper object, method
> eval %{
> def object.#{method}
> # do something here
> super # call the wrapped method
> end
> }
> end


sorry the above code does not work, (needs to be done using
object.instance_eval) but you get the idea what i mean

# example of usage:
> make_wrapper STDOUT, :puts
>
> using eval works, but it seems not to be the best solution. is there
> annother way do define methods from a given symbol?
>
> -- henon
>
>

Robert Klemme

3/7/2006 9:44:00 AM

0

Meinrad Recheis wrote:
> hello fellow rubyists,
>
> is there an elegant way to define a singleton method from a given
> symbol without using eval? what i am doing is this:
>
> def make_wrapper object, method
> eval %{
> def object.#{method}
> # do something here
> super # call the wrapped method
> end
> }
> end
>
> # example of usage:
> make_wrapper STDOUT, :puts
>
> using eval works, but it seems not to be the best solution. is there
> annother way do define methods from a given symbol?

Are you sure the code you presented actually works? IMHO your code will
fail if the method is defined in the same class (i.e. no "super"
possible).

You could use Delegator for this. And, if the method you want to wrap
does not use a block define_method usually works quite well.

Kind regards

robert

Meinrad Recheis

3/7/2006 10:03:00 AM

0

On 3/7/06, Robert Klemme <bob.news@gmx.net> wrote:
>
> Meinrad Recheis wrote:
> [snipped]
>
> Are you sure the code you presented actually works? IMHO your code will
> fail if the method is defined in the same class (i.e. no "super"
> possible).


afaik calling super in a singleton method calls the overridden method of
that object (of course i assert that the method to be wrapped exists).
here is the working code snippet:
def make_wrapper object, method
object.instance_eval %{
def self.#{method}(*args, &block)
puts "wrapped method #{method}"
super
end
}
end

You could use Delegator for this. And, if the method you want to wrap
> does not use a block define_method usually works quite well.


ah, object.send( :define_method) is what i was looking for. thanks

Kind regards
>
> robert
>
>
>