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Uko2

Spaceship?

Hi everyone.

I’m wandering if there was any sort of a discussion about a spaceship method used in Ruby.

The concept is that you should implement a method <=>
that returns something negative if the receiver is smaller then a parameter,
positive when the receiver is greater then a parameter,
and 0 if they are equal.

This way if you are implementing comparable object’s the only method you have to redefine is spaceship (<=>).

Yes, I know that i Pharo you have to only redefine < and =. But maybe it would be interesting to use spaceship :)

What do you think?
Cheers!
Uko

Stéphane Ducasse

Re: Spaceship?

do you have a real use case?

Stef

On Nov 4, 2013, at 1:32 PM, Yuriy Tymchuk <[hidden email]> wrote:

> Hi everyone.
>
> I’m wandering if there was any sort of a discussion about a spaceship method used in Ruby.
>
> The concept is that you should implement a method <=>
> that returns something negative if the receiver is smaller then a parameter,
> positive when the receiver is greater then a parameter,
> and 0 if they are equal.
>
> This way if you are implementing comparable object’s the only method you have to redefine is spaceship (<=>).
>
> Yes, I know that i Pharo you have to only redefine < and =. But maybe it would be interesting to use spaceship :)
>
> What do you think?
> Cheers!
> Uko

philippeback

Re: Spaceship?

Type and double dispatch + nil considérations come to mind.

nil <=> 7 gives?

7.0 <=> 3 gives ?

Object <=>: anObject

(self = anObject) ifTrue: [ ^0].

(self < anObject) ifTrue: [ ^ -1] ifFalse: [ ^ 1].

"otherwise let's raise an error"

What can now go wrong from here ?

Phil
On Monday, November 4, 2013, Stéphane Ducasse wrote:

do you have a real use case?

Stef

On Nov 4, 2013, at 1:32 PM, Yuriy Tymchuk <<a href="javascript:;" onclick="_e(event, 'cvml', 'yuriy.tymchuk@me.com')">yuriy.tymchuk@...> wrote:

> Hi everyone.
>
> I’m wandering if there was any sort of a discussion about a spaceship method used in Ruby.
>
> The concept is that you should implement a method <=>
> that returns something negative if the receiver is smaller then a parameter,
> positive when the receiver is greater then a parameter,
> and 0 if they are equal.
>
> This way if you are implementing comparable object’s the only method you have to redefine is spaceship (<=>).
>
> Yes, I know that i Pharo you have to only redefine < and =. But maybe it would be interesting to use spaceship :)
>
> What do you think?
> Cheers!
> Uko

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Uko2

Re: Spaceship?

In reply to this post by Stéphane Ducasse

Now she someone want’s to have a comparable object he has to use TComparable and define < and =.
With spaceship he has to define only <=>. I’m not sure what’s better. Just wanted to hear other peoples opinion

On 04 Nov 2013, at 13:35, Stéphane Ducasse <[hidden email]> wrote:

> do you have a real use case?
>
> Stef
>
> On Nov 4, 2013, at 1:32 PM, Yuriy Tymchuk <[hidden email]> wrote:
>
>> Hi everyone.
>>
>> I’m wandering if there was any sort of a discussion about a spaceship method used in Ruby.
>>
>> The concept is that you should implement a method <=>
>> that returns something negative if the receiver is smaller then a parameter,
>> positive when the receiver is greater then a parameter,
>> and 0 if they are equal.
>>
>> This way if you are implementing comparable object’s the only method you have to redefine is spaceship (<=>).
>>
>> Yes, I know that i Pharo you have to only redefine < and =. But maybe it would be interesting to use spaceship :)
>>
>> What do you think?
>> Cheers!
>> Uko
>
>

kilon.alios

Re: Spaceship?

It looks to me that this would be the source of less readable code, I prefer the choosing message approach by Kent Beck (Smalltalk Best Practice Patterns) where intent is clearly stated. Unless there is an advantage I am missing here. This is an example that less verbose code does not mean simpler code. Of course this will largely depend on the specifics of the case used.

On Mon, Nov 4, 2013 at 3:37 PM, Yuriy Tymchuk <[hidden email]> wrote:

Now she someone want’s to have a comparable object he has to use TComparable and define < and =.
With spaceship he has to define only <=>. I’m not sure what’s better. Just wanted to hear other peoples opinion

On 04 Nov 2013, at 13:35, Stéphane Ducasse <[hidden email]> wrote:

> do you have a real use case?
>
> Stef
>
> On Nov 4, 2013, at 1:32 PM, Yuriy Tymchuk <[hidden email]> wrote:
>
>> Hi everyone.
>>
>> I’m wandering if there was any sort of a discussion about a spaceship method used in Ruby.
>>
>> The concept is that you should implement a method <=>
>> that returns something negative if the receiver is smaller then a parameter,
>> positive when the receiver is greater then a parameter,
>> and 0 if they are equal.
>>
>> This way if you are implementing comparable object’s the only method you have to redefine is spaceship (<=>).
>>
>> Yes, I know that i Pharo you have to only redefine < and =. But maybe it would be interesting to use spaceship :)
>>
>> What do you think?
>> Cheers!
>> Uko
>
>

Nicolas Cellier

Re: Spaceship?

Beware of cases where you don't have total order.

For example, in recent Squeak/Pharo we add to redefine the whole set of operators on numbers, not only < and =, just because NaN is not ordered...

2013/11/4 kilon alios <[hidden email]>

It looks to me that this would be the source of less readable code, I prefer the choosing message approach by Kent Beck (Smalltalk Best Practice Patterns) where intent is clearly stated. Unless there is an advantage I am missing here. This is an example that less verbose code does not mean simpler code. Of course this will largely depend on the specifics of the case used.

On Mon, Nov 4, 2013 at 3:37 PM, Yuriy Tymchuk <[hidden email]> wrote:

Now she someone want’s to have a comparable object he has to use TComparable and define < and =.
With spaceship he has to define only <=>. I’m not sure what’s better. Just wanted to hear other peoples opinion

On 04 Nov 2013, at 13:35, Stéphane Ducasse <[hidden email]> wrote:

> do you have a real use case?
>
> Stef
>
> On Nov 4, 2013, at 1:32 PM, Yuriy Tymchuk <[hidden email]> wrote:
>
>> Hi everyone.
>>
>> I’m wandering if there was any sort of a discussion about a spaceship method used in Ruby.
>>
>> The concept is that you should implement a method <=>
>> that returns something negative if the receiver is smaller then a parameter,
>> positive when the receiver is greater then a parameter,
>> and 0 if they are equal.
>>
>> This way if you are implementing comparable object’s the only method you have to redefine is spaceship (<=>).
>>
>> Yes, I know that i Pharo you have to only redefine < and =. But maybe it would be interesting to use spaceship :)
>>
>> What do you think?
>> Cheers!
>> Uko
>
>

Nicolas Cellier

Re: Spaceship?

we add^H^H^H had

2013/11/4 Nicolas Cellier <[hidden email]>

Beware of cases where you don't have total order.
For example, in recent Squeak/Pharo we add to redefine the whole set of operators on numbers, not only < and =, just because NaN is not ordered...

2013/11/4 kilon alios <[hidden email]>

It looks to me that this would be the source of less readable code, I prefer the choosing message approach by Kent Beck (Smalltalk Best Practice Patterns) where intent is clearly stated. Unless there is an advantage I am missing here. This is an example that less verbose code does not mean simpler code. Of course this will largely depend on the specifics of the case used.

On Mon, Nov 4, 2013 at 3:37 PM, Yuriy Tymchuk <[hidden email]> wrote:

Now she someone want’s to have a comparable object he has to use TComparable and define < and =.
With spaceship he has to define only <=>. I’m not sure what’s better. Just wanted to hear other peoples opinion

On 04 Nov 2013, at 13:35, Stéphane Ducasse <[hidden email]> wrote:

> do you have a real use case?
>
> Stef
>
> On Nov 4, 2013, at 1:32 PM, Yuriy Tymchuk <[hidden email]> wrote:
>
>> Hi everyone.
>>
>> I’m wandering if there was any sort of a discussion about a spaceship method used in Ruby.
>>
>> The concept is that you should implement a method <=>
>> that returns something negative if the receiver is smaller then a parameter,
>> positive when the receiver is greater then a parameter,
>> and 0 if they are equal.
>>
>> This way if you are implementing comparable object’s the only method you have to redefine is spaceship (<=>).
>>
>> Yes, I know that i Pharo you have to only redefine < and =. But maybe it would be interesting to use spaceship :)
>>
>> What do you think?
>> Cheers!
>> Uko
>
>

Uko2

Re: Spaceship?

In reply to this post by Nicolas Cellier

No one prohibits you from redefining other operators.

It’s just that a > b is defined by default as b < a. So why it is this way and not a < b is b > a ;)

With spaceship there is one method to rule them all. But Pharo’s implementation is interesting too. I never had an idea that you can define things like that

On 04 Nov 2013, at 18:54, Nicolas Cellier <[hidden email]> wrote:

Beware of cases where you don't have total order.
For example, in recent Squeak/Pharo we add to redefine the whole set of operators on numbers, not only < and =, just because NaN is not ordered...

2013/11/4 kilon alios <[hidden email]>

It looks to me that this would be the source of less readable code, I prefer the choosing message approach by Kent Beck (Smalltalk Best Practice Patterns) where intent is clearly stated. Unless there is an advantage I am missing here. This is an example that less verbose code does not mean simpler code. Of course this will largely depend on the specifics of the case used.

On Mon, Nov 4, 2013 at 3:37 PM, Yuriy Tymchuk <[hidden email]> wrote:

Now she someone want’s to have a comparable object he has to use TComparable and define < and =.
With spaceship he has to define only <=>. I’m not sure what’s better. Just wanted to hear other peoples opinion

On 04 Nov 2013, at 13:35, Stéphane Ducasse <[hidden email]> wrote:

> do you have a real use case?
>
> Stef
>
> On Nov 4, 2013, at 1:32 PM, Yuriy Tymchuk <[hidden email]> wrote:
>
>> Hi everyone.
>>
>> I’m wandering if there was any sort of a discussion about a spaceship method used in Ruby.
>>
>> The concept is that you should implement a method <=>
>> that returns something negative if the receiver is smaller then a parameter,
>> positive when the receiver is greater then a parameter,
>> and 0 if they are equal.
>>
>> This way if you are implementing comparable object’s the only method you have to redefine is spaceship (<=>).
>>
>> Yes, I know that i Pharo you have to only redefine < and =. But maybe it would be interesting to use spaceship :)
>>
>> What do you think?
>> Cheers!
>> Uko
>
>