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From: David A. Black on 6 Jun 2010 20:55
Hi --

On Mon, 7 Jun 2010, Rein Henrichs wrote:

> In addition to the previously mentioned difference between #methods and
> #instance_methods, #inject is actually a method on the Enumerable module,
> which is mixed into Array (and other classes that have #each). The Enumerable
> module is full of methods that can be used on "things that can enumerate
> themselves", like Arrays, Hashes and Sets.

Although a surprising (to me) number of Enumerable's instance methods
are overridden in Array:

irb(main):008:0> (Array.instance_methods(false) &
Enumerable.instance_methods).sort
=> ["collect", "count", "cycle", "drop", "drop_while", "find_index",
"first", "include?", "map", "reject", "reverse_each", "select",
"sort", "take", "take_while", "to_a", "zip"]

(That's 1.8.7 but the list is the same in 1.9.1.)


David

--
David A. Black, Senior Developer, Cyrus Innovation Inc.

THE Ruby training with Black/Brown/McAnally
COMPLEAT Coming to Chicago area, June 18-19, 2010!
RUBYIST http://www.compleatrubyist.com

From: Rein Henrichs on 6 Jun 2010 21:22
On 2010-06-06 17:55:58 -0700, David A. Black said:

> Hi --
>
> On Mon, 7 Jun 2010, Rein Henrichs wrote:
>
>> In addition to the previously mentioned difference between #methods and
>> #instance_methods, #inject is actually a method on the Enumerable module,
>> which is mixed into Array (and other classes that have #each). The Enumerable
>> module is full of methods that can be used on "things that can enumerate
>> themselves", like Arrays, Hashes and Sets.
>
> Although a surprising (to me) number of Enumerable's instance methods
> are overridden in Array:
>
> irb(main):008:0> (Array.instance_methods(false) &
> Enumerable.instance_methods).sort
> => ["collect", "count", "cycle", "drop", "drop_while", "find_index",
> "first", "include?", "map", "reject", "reverse_each", "select",
> "sort", "take", "take_while", "to_a", "zip"]
>
> (That's 1.8.7 but the list is the same in 1.9.1.)
>
>
> David

I suspect that the majority are overwritten for performance reasons,
although some of them surprise me as well.

A linked list, for instance, would have a constant time #count because
that state is kept on the list object and doesn't require an O(n)
enumeration of the members.

--
Rein Henrichs
http://puppetlabs.com
http://reinh.com

From: RichardSchollar on 7 Jun 2010 00:29
Thanks everyone - I appreciate all the responses and it has clarified
what I was seeing.

From: David A. Black on 7 Jun 2010 05:42
Hi --

On Mon, 7 Jun 2010, Rein Henrichs wrote:

> On 2010-06-06 17:55:58 -0700, David A. Black said:
>
>> Hi --
>>
>> On Mon, 7 Jun 2010, Rein Henrichs wrote:
>>
>>> In addition to the previously mentioned difference between #methods and
>>> #instance_methods, #inject is actually a method on the Enumerable module,
>>> which is mixed into Array (and other classes that have #each). The
>>> Enumerable
>>> module is full of methods that can be used on "things that can enumerate
>>> themselves", like Arrays, Hashes and Sets.
>>
>> Although a surprising (to me) number of Enumerable's instance methods
>> are overridden in Array:
>>
>> irb(main):008:0> (Array.instance_methods(false) &
>> Enumerable.instance_methods).sort
>> => ["collect", "count", "cycle", "drop", "drop_while", "find_index",
>> "first", "include?", "map", "reject", "reverse_each", "select",
>> "sort", "take", "take_while", "to_a", "zip"]
>>
>> (That's 1.8.7 but the list is the same in 1.9.1.)
>>
>>
>> David
>
> I suspect that the majority are overwritten for performance reasons, although
> some of them surprise me as well.
>
> A linked list, for instance, would have a constant time #count because that
> state is kept on the list object and doesn't require an O(n) enumeration of
> the members.

I think it's a mixture of performance reasons and things like what it
should return if there's no block (like Enumerable#map always
returning an array vs. Array#map returning its receiver). Array is
definitely the one that has the most overrides, with Hash coming in
second at 6 and IO having none.


David

--
David A. Black, Senior Developer, Cyrus Innovation Inc.

THE Ruby training with Black/Brown/McAnally
COMPLEAT Coming to Chicago area, June 18-19, 2010!
RUBYIST http://www.compleatrubyist.com

From: Robert Klemme on 7 Jun 2010 07:46
2010/6/7 David A. Black <dblack(a)rubypal.com>:

> On Mon, 7 Jun 2010, Rein Henrichs wrote:
>
>> On 2010-06-06 17:55:58 -0700, David A. Black said:

>> I suspect that the majority are overwritten for performance reasons,
>> although some of them surprise me as well.
>>
>> A linked list, for instance, would have a constant time #count because
>> that state is kept on the list object and doesn't require an O(n)
>> enumeration of the members.
>
> I think it's a mixture of performance reasons and things like what it
> should return if there's no block (like Enumerable#map always
> returning an array vs. Array#map returning its receiver). Array is
> definitely the one that has the most overrides, with Hash coming in
> second at 6 and IO having none.

David, I guess you meant to write "... vs. Array#map! returning its
receiver"? Note the exclamation mark. Array#map returns a new Array
on every invocation.

Kind regards

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

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