Define a function inside a method

Ruby
1

Hi,

I wrote a method which uses recursion, internally. As a test, I tried to
define the recursive function inside the method that is called :

class Ga
def bu
def zo(n)
# recursively call zo
end
10.times {|n| zo(n)}
end

At my surprise, this code ran well ! But I wonder if this is a good
idea…
Should I be aware of possible problems, or limitations, coming from
this
kind of construction ? I can’t figure out where the zo function
actually “lives”.

Thanks.

2

On 03.03.2007 15:41, Olivier R. wrote:

10.times {|n| zo(n)}
end

At my surprise, this code ran well ! But I wonder if this is a good idea…
Should I be aware of possible problems, or limitations, coming from this
kind of construction ? I can’t figure out where the zo function
actually “lives”.

The issue here is (apart from the missing “end” in your piece above)
that zo will be defined every time you execute bu - that’s probably not
something you want as it is inefficient and you do not actually change
zu’s definition. Also, zo becomes a normal method - there is no such
thing as a nested method in Ruby:

irb(main):001:0> class Ga
irb(main):002:1> def bu
irb(main):003:2> def zo(n)
irb(main):004:3> # recursively call zo
irb(main):005:3* end
irb(main):006:2> 10.times {|n| zo(n)}
irb(main):007:2> end
irb(main):008:1> end
=> nil
irb(main):009:0> Ga.new.zo 1
NoMethodError: undefined method `zo’ for #Ga:0x39ba98
from (irb):9
from :0
irb(main):010:0> Ga.new.bu
=> 10
irb(main):011:0> Ga.new.zo 1
=> nil

Kind regards

robert

3

Le samedi 03 mars 2007 16:10, Robert K. a écrit :

end

something you want as it is inefficient and you do not actually change
irb(main):008:1> end
Kind regards

robert

Thanks, this is perfectly clear !
Finally, I rewrote this method to avoid the recursion, since it was a
tail
recursion.

4

Olivier R. schrieb:

I wrote a method which uses recursion, internally. As a test, I tried to
define the recursive function inside the method that is called :

class Ga
def bu
def zo(n)
# recursively call zo
end
10.times {|n| zo(n)}
end

In addition to the other answers, if you really want method-internal
methods, you can use lambdas:

class Ga
def bu
zo = lambda {|n|
# recursively call zo
}
10.times {|n| zo.call(n)}
end
end

Regards,
Pit

5

On Mar 3, 7:41 am, Olivier R. [email protected] wrote:

I wrote a method which uses recursion, internally. As a test, I tried to
define the recursive function inside the method that is called :

Time to investigate:

class Foo
def bar
p jim rescue p “no jim yet”
def jim; “jim”; end
jim
end
end

f1 = Foo.new

p f1.jim rescue p “no jim yet”
#=> “no jim yet”

p f1.bar
#=> “no jim yet”
#=> “jim”

p f1.jim
#=> “jim”

f2 = Foo.new
p f2.jim
#=> “jim”

p f1.method( :jim )
#=> #<Method: Foo#jim>

What I deduce from this is that running Foo#bar causes a new instance
method “jim” to be defined for the Foo class. The only thing this gets
you is delayed method realization, once only, per class. It’s not a
private function for the use by that method only.