why doesn't Array include Comparable

[ara.t.howard]

why __wouldn't__ one want this?



harp:~ > cat a.rb
a = 0,1,2
b = 2,3,4

p a < b rescue puts "can't do that!"

class Array; include Comparable; end

p a < b


harp:~ > ruby a.rb
can't do that!
true

??


-a

 

[Hal Fulton]

why __wouldn't__ one want this?



harp:~ > cat a.rb
a = 0,1,2
b = 2,3,4

p a < b rescue puts "can't do that!"

class Array; include Comparable; end

p a < b


harp:~ > ruby a.rb
can't do that!
true

??

Offhand I would guess it's because arrays can
hold arbitrary objects.

If one array held four different classes of
objects, and another held yet another four
classes of objects, that's potentially sixteen
spaceship operators that would need to be
defined for this to make sense. And most of
those would not make sense anyway.


Hal

 

[Logan Capaldo]

Offhand I would guess it's because arrays can
hold arbitrary objects.

If one array held four different classes of
objects, and another held yet another four
classes of objects, that's potentially sixteen
spaceship operators that would need to be
defined for this to make sense. And most of
those would not make sense anyway.

But spaceship is already defined for array (and it does the right
thing (tm)). If Array is going to make spaceship available, why _not_
include Comparable?

 

[James Edward Gray II]

But spaceship is already defined for array (and it does the right
thing (tm)). If Array is going to make spaceship available, why
_not_ include Comparable?

I have to agree. I know I've wanted it a couple of times now.

James Edward Gray II

 

[Trans]

Indeed I have found it useful to

class Tuple < Array
include Comparable
end

But I also make it immutable.

T.

 

[ara.t.howard]

Offhand I would guess it's because arrays can
hold arbitrary objects.

If one array held four different classes of
objects, and another held yet another four
classes of objects, that's potentially sixteen
spaceship operators that would need to be
defined for this to make sense. And most of
those would not make sense anyway.

i don't understand - it's up to to the objects inside the container to
impliment the right methods and array already knows how to handle it:


harp:~ > cat a.rb
a = 0, 'foo', 42
b = 1, 'bar', 42.0

p a < b rescue puts "can't do that"

class Array; include Comparable; end

p a < b

p a.sort_by{ rand } < b.sort_by{ rand }


harp:~ > ruby a.rb
can't do that
true
a.rb:9:in `<': comparison of Array with Array failed (ArgumentError)
from a.rb:9


if you're collections impliment <=> correctly then Array does the right thing -
looping over each of them.

-a

 

[ara.t.howard]

But spaceship is already defined for array (and it does the right thing
(tm)). If Array is going to make spaceship available, why _not_ include
Comparable?

yeah - exactly. by implimenting <=> it __is__ comparable in that one can
indeed to

a = 0,1,2
b = 2,3,4

lt = (a <=> b) == -1
eq = (a <=> b) == 0
gt = (a <=> b) == 1

so it's just anoying that i can't acutally say

lt = a < b

2 cts.

-a

 

[Daniel Berger]

On Wed, 9 Aug 2006, Hal Fulton wrote:
=20
=20
i don't understand - it's up to to the objects inside the container to
impliment the right methods and array already knows how to handle it:
=20
=20
harp:~ > cat a.rb
a =3D 0, 'foo', 42
b =3D 1, 'bar', 42.0
=20
p a < b rescue puts "can't do that"
=20
class Array; include Comparable; end
=20
p a < b
=20
p a.sort_by{ rand } < b.sort_by{ rand }
=20
=20
harp:~ > ruby a.rb
can't do that
true
a.rb:9:in `<': comparison of Array with Array failed (ArgumentError)
from a.rb:9
=20
=20
if you're collections impliment <=3D> correctly then Array does the = right=20
thing -
looping over each of them.
=20
-a

FWIW, I modified the Array class to include Comparable and then ran both =
the=20
test_array.rb file that's distributed with the Ruby distro and my own =
tests in=20
the ruby_test project and all tests still passed.

Regards,

Dan


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