Asp Forum - Method Precedence

Daly

2/6/2009 3:05:00 AM

Hello all,

If I have a class such as:

class Example

def one
puts "one"

def two
puts "two inside one"
end
end

def two
puts "two inside Example"
end

end

And I do:
e = Example.new
e.one
e.two

I get, obviously:
one
two inside one

What I don't understand is that if after that I do:
f = Example.new
f.two

I still get:
two inside one

Since the two method in question is defined within one, doesn't it
behave like a method on the object e? How can it override the two
method outside for the f object?

Thanks for your help in explaining this.

14 Answers

Phlip

2/6/2009 3:18:00 AM

Daly wrote:

> Hello all,
>
> If I have a class such as:
>
> class Example
>
> def one
> puts "one"
>
> def two
> puts "two inside one"
> end
> end
>
> def two
> puts "two inside Example"
> end
>
> end
>
> And I do:
> e = Example.new
> e.one
> e.two
>
> I get, obviously:
> one
> two inside one
>
> What I don't understand is that if after that I do:
> f = Example.new
> f.two
>
> I still get:
> two inside one

When the compiler first encountered Example, it plugged one() and the outer
two() into Example's class instance list.

The first call to one() then bonds the inner two() to the class. The object did
not get affected in either case. (Always remember classes are objects around here!)

If you ran the program again (a new Ruby "VM"), and never called one(), you
would only get the outer two().

--
Phlip

Julian Leviston

2/6/2009 3:27:00 AM

What happens when you call the one method is it redefines the two
INSTANCE METHOD at the class level (ie the context of instance method
definition in the class), which means ALL objects are affected.

Why would you want to do this?

Julian.

On 06/02/2009, at 2:05 PM, Daly wrote:

> Hello all,
>
> If I have a class such as:
>
> class Example
>
> def one
> puts "one"
>
> def two
> puts "two inside one"
> end
> end
>
> def two
> puts "two inside Example"
> end
>
> end
>
> And I do:
> e = Example.new
> e.one
> e.two
>
> I get, obviously:
> one
> two inside one
>
> What I don't understand is that if after that I do:
> f = Example.new
> f.two
>
> I still get:
> two inside one
>
> Since the two method in question is defined within one, doesn't it
> behave like a method on the object e? How can it override the two
> method outside for the f object?
>
> Thanks for your help in explaining this.
>

Julian Leviston

2/6/2009 3:27:00 AM

FYI, it's not a compiler, it's an interpreter.

Also, by "the object did not get affected" you mean the instance
object... just to clarify for him.

Julian.

On 06/02/2009, at 2:19 PM, Phlip wrote:

> When the compiler first encountered Example, it plugged one() and
> the outer two() into Example's class instance list.
>
> The first call to one() then bonds the inner two() to the class. The
> object did not get affected in either case. (Always remember classes
> are objects around here!)
>
> If you ran the program again (a new Ruby "VM"), and never called
> one(), you would only get the outer two().

Phlip

2/6/2009 3:46:00 AM

Julian Leviston wrote:

> FYI, it's not a compiler, it's an interpreter.

The terms "compiler" and "interpreter" have never been exclusive - ask a Lisper!

--
Phlip

Daly

2/6/2009 3:47:00 AM

I'm doing this as a learning experiment. I would have thought that
since self inside method one is an object, then two inside one would
be defined on the object, not on the class.

Phlip's explanation made it clear to me though. It's as if I opened
the class and redefined two, correct?

On Feb 5, 10:26=A0pm, Julian Leviston <jul...@coretech.net.au> wrote:
> What happens when you call the one method is it redefines the two =A0
> INSTANCE METHOD at the class level (ie the context of instance method =A0
> definition in the class), which means ALL objects are affected.
>
> Why would you want to do this?
>
> Julian.
>
> On 06/02/2009, at 2:05 PM, Daly wrote:
>
> > Hello all,
>
> > If I have a class such as:
>
> > class Example
>
> > =A0def one
> > =A0 =A0puts "one"
>
> > =A0 =A0def two
> > =A0 =A0 =A0puts "two inside one"
> > =A0 =A0end
> > =A0end
>
> > =A0def two
> > =A0 =A0puts "two inside Example"
> > =A0end
>
> > end
>
> > And I do:
> > e =3D Example.new
> > e.one
> > e.two
>
> > I get, obviously:
> > one
> > two inside one
>
> > What I don't understand is that if after that I do:
> > f =3D Example.new
> > f.two
>
> > I still get:
> > two inside one
>
> > Since the two method in question is defined within one, doesn't it
> > behave like a method on the object e? How can it override the two
> > method outside for the f object?
>
> > Thanks for your help in explaining this.
>
>

Phlip

2/6/2009 4:04:00 AM

Daly wrote:

> Phlip's explanation made it clear to me though. It's as if I opened
> the class and redefined two, correct?

Yes - always think of the interpreter like a text caret skipping thru the
program, statement by statement, from top to bottom. It interprets 'class' and
'def', but it only parses what's inside the def, and stores it. The interpreter
can't even see the inner 'too()' (except as lexically correct tokens). Only when
you call 'one()' does the interpreter go back inside and this time actually
execute its lines.

Julian Leviston

2/6/2009 4:21:00 AM

No

The method is on the class, as an istnce method. There is only one
class, and all instances look to it for their methods. If you want you
can do methods on particular instances only. You probably want this
behaviour and I think it's achieved with instance_eval. I'll post an
example in a sec

Blog: http://random8.ze...
Learn rails: http://sensei.ze...

On 06/02/2009, at 2:46 PM, Daly <aeldaly@gmail.com> wrote:

> I'm doing this as a learning experiment. I would have thought that
> since self inside method one is an object, then two inside one would
> be defined on the object, not on the class.
>
> Phlip's explanation made it clear to me though. It's as if I opened
> the class and redefined two, correct?
>
> On Feb 5, 10:26 pm, Julian Leviston <jul...@coretech.net.au> wrote:
>> What happens when you call the one method is it redefines the two
>> INSTANCE METHOD at the class level (ie the context of instance method
>> definition in the class), which means ALL objects are affected.
>>
>> Why would you want to do this?
>>
>> Julian.
>>
>> On 06/02/2009, at 2:05 PM, Daly wrote:
>>
>>> Hello all,
>>
>>> If I have a class such as:
>>
>>> class Example
>>
>>> def one
>>> puts "one"
>>
>>> def two
>>> puts "two inside one"
>>> end
>>> end
>>
>>> def two
>>> puts "two inside Example"
>>> end
>>
>>> end
>>
>>> And I do:
>>> e = Example.new
>>> e.one
>>> e.two
>>
>>> I get, obviously:
>>> one
>>> two inside one
>>
>>> What I don't understand is that if after that I do:
>>> f = Example.new
>>> f.two
>>
>>> I still get:
>>> two inside one
>>
>>> Since the two method in question is defined within one, doesn't it
>>> behave like a method on the object e? How can it override the two
>>> method outside for the f object?
>>
>>> Thanks for your help in explaining this.
>>
>>
>

Julian Leviston

2/6/2009 4:23:00 AM

Yeah, it's as if you opened the class and redefined two... you're right.

if you want to define the method only on the particular instance that
you run that one method on you can do something like this:

hope this helps.

Last login: Fri Feb 6 14:06:35 on ttys003
Phatty:~ julian$ irb
>> class Hi
>> def one
>> instance_eval("
def two
puts 'hi'
end
")
>> end
>> def two
>> puts 'woo'
>> end
>> end
=> nil
>> x = Hi.new
=> #<Hi:0x5eab78>
>> y = Hi.new
=> #<Hi:0x5e96b0>
>> x.two
woo
=> nil
>> y.two
woo
=> nil
>> x.one
=> nil
>> x.two
hi
=> nil
>> y.two
woo
=> nil
>>

On 06/02/2009, at 2:46 PM, Daly wrote:

> I'm doing this as a learning experiment. I would have thought that
> since self inside method one is an object, then two inside one would
> be defined on the object, not on the class.
>
> Phlip's explanation made it clear to me though. It's as if I opened
> the class and redefined two, correct?
>
> On Feb 5, 10:26 pm, Julian Leviston <jul...@coretech.net.au> wrote:
>> What happens when you call the one method is it redefines the two
>> INSTANCE METHOD at the class level (ie the context of instance method
>> definition in the class), which means ALL objects are affected.
>>
>> Why would you want to do this?
>>
>> Julian.
>>
>> On 06/02/2009, at 2:05 PM, Daly wrote:
>>
>>> Hello all,
>>
>>> If I have a class such as:
>>
>>> class Example
>>
>>> def one
>>> puts "one"
>>
>>> def two
>>> puts "two inside one"
>>> end
>>> end
>>
>>> def two
>>> puts "two inside Example"
>>> end
>>
>>> end
>>
>>> And I do:
>>> e = Example.new
>>> e.one
>>> e.two
>>
>>> I get, obviously:
>>> one
>>> two inside one
>>
>>> What I don't understand is that if after that I do:
>>> f = Example.new
>>> f.two
>>
>>> I still get:
>>> two inside one
>>
>>> Since the two method in question is defined within one, doesn't it
>>> behave like a method on the object e? How can it override the two
>>> method outside for the f object?
>>
>>> Thanks for your help in explaining this.
>>
>>
>

Bertram Scharpf

2/6/2009 4:23:00 AM

Am Freitag, 06. Feb 2009, 12:05:21 +0900 schrieb Daly:
> class Example
> def one
> puts "one"
> def two
> puts "two inside one"
> end
> end
> def two
> puts "two inside Example"
> end
> end
>
> e = Example.new
> e.one
> e.two
> f = Example.new
> f.two

In case you just want to influence the e object, say

class Example
def one
puts "one"
def self.two
# ^^^^^
puts "two inside one"
end
end
end

Bertram

--
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-...

pjb

2/6/2009 4:23:00 AM

Daly <aeldaly@gmail.com> writes:

> I'm doing this as a learning experiment. I would have thought that
> since self inside method one is an object, then two inside one would
> be defined on the object, not on the class.
>
> Phlip's explanation made it clear to me though. It's as if I opened
> the class and redefined two, correct?

Yes.

def ... end is not a definition. It's an expression. It is executed,
and it has side effects.

--
__Pascal Bourguignon__

comp.lang.ruby

Method Precedence

Daly

Phlip

Julian Leviston

Julian Leviston

Phlip

Daly

Phlip

Julian Leviston

Julian Leviston

Bertram Scharpf

pjb

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