Nested methods

Ruby
1

Hi,

This example is from pickaxe2(I can’t find the page):

def toggle

def toggle
puts “subsequent”
end

puts “first”
end

toggle
toggle
toggle

–output:–
first
subsequent
subsequent

Can someone explain why the nested method hides the outer method?

Thanks.

2

2009/3/20 7stud – [email protected]

puts “first”

Can someone explain why the nested method hides the outer method?

The first call redefines toggle on the current object (which here seems
to
be the global main object) and then returns “first”. After this, toggle
has
been replaced by the inner method so it returns “subsequent” for all
further
calls.

3

Can someone explain why the nested method hides the outer method?

There are no nested methods in ruby (similar to smalltalk, eiffel,
java and unlike scheme, python etc.).

4

2009/3/20 Leo [email protected]

Can someone explain why the nested method hides the outer method?

There are no nested methods in ruby (similar to smalltalk, eiffel,
java and unlike scheme, python etc.).

This statement could confuse people given the above. Clearly you can
define
methods inside other methods, the point is that the ‘inner’ method is
not
local to the outer one. The inner one becomes defined in the same scope
as
the outer one, and does not remember the environment it was created in.
Methods are not closures, unlike blocks/procs/lambdas.

5

2009/3/20 Brian A. [email protected]

and does not remember the environment it was created in.
Methods are not closures, unlike blocks/procs/lambdas.

Depends what you mean by nesting, which was supposed to be my point –
that
the methods are lexically nested but not dynamically nested. In other
words
their lexical nesting does not imply lexical scope or closures in this
case.

6

Depends what you mean by nesting, which was supposed to be my point – that
the methods are lexically nested but not dynamically nested.

I don’t think I understand what you mean with “lexically nested” here.
The point is that the inner method replaces the outer one. Nothing
else. Maybe we could call that stacked methods or whatever. But since
the inner method cannot refer to local variables of the outer method
the word nested IMHO simply makes no sense.

The reason why I posted my possibly confusing statement was because
when I started using ruby, I was myself confused by the lack of nested
methods in ruby. It became easier for me to code in ruby after I
simply accepted that ruby doesn’t have nested methods/functions like
many functional languages.

7

James C. [email protected] writes:

This statement could confuse people given the above. Clearly you can define
methods inside other methods, the point is that the ‘inner’ method is not
local to the outer one. The inner one becomes defined in the same scope as
the outer one,

Isn’t being defined in the same scope the antithesis of nesting?

8

2009/3/20 Leo [email protected]

Depends what you mean by nesting, which was supposed to be my point –
that
the methods are lexically nested but not dynamically nested.

I don’t think I understand what you mean with “lexically nested” here.
The point is that the inner method replaces the outer one. Nothing
else. Maybe we could call that stacked methods or whatever. But since
the inner method cannot refer to local variables of the outer method
the word nested IMHO simply makes no sense.

I meant ‘lexically’ as in the methods are syntactically nested. You’re
right, since methods are not closures it makes no sense to talk of them
as
being nested/stacked/whatever when talking about how the code is
executed,
they are nested in appearance only.