I talked to a programmer who knows Scala (among others) and he mentioned the usefulness of the Option type - a zero or one element collection (range in D terminology). Here's an article discussing it: http://danielwestheide.com/blog/2012/12/19/the-neophytes-guide-to-scala-part-5-the-option-type.html

We have only(x) (http://dlang.org/phobos/std_range.html#.only) to be a collection of exactly one value, but not a type for "a value of type T or nothing at all". Should we follow Scala's example and add it?


Andrei

On Tuesday, 10 December 2013 at 17:28:26 UTC, Andrei Alexandrescu wrote:
> We have only(x) (http://dlang.org/phobos/std_range.html#.only) to be a collection of exactly one value, but not a type for "a value of type T or nothing at all".

Is this not what Nullable!T is?

On 2013-12-10 17:28:26 +0000, Andrei Alexandrescu said:

> I talked to a programmer who knows Scala (among others) and he mentioned the usefulness of the Option type - a zero or one element collection (range in D terminology). Here's an article discussing it: http://danielwestheide.com/blog/2012/12/19/the-neophytes-guide-to-scala-part-5-the-option-type.html 
> 
> 
> We have only(x) (http://dlang.org/phobos/std_range.html#.only) to be a collection of exactly one value, but not a type for "a value of type T or nothing at all". Should we follow Scala's example and add it?
> 
> 
> Andrei

Yes! Option is super useful. Use it all the time in Scala and Java (via Guava library).
I suppose it will be defined as a range, so map will work on it?
One of the useful things about options are the ability to chain them via flatMap, will this usecase be handled?

On Tuesday, 10 December 2013 at 17:28:26 UTC, Andrei Alexandrescu wrote:
> I talked to a programmer who knows Scala (among others) and he mentioned the usefulness of the Option type - a zero or one element collection (range in D terminology). Here's an article discussing it: http://danielwestheide.com/blog/2012/12/19/the-neophytes-guide-to-scala-part-5-the-option-type.html

I really came to love Option when I was working in F#.  One of the things I love about F# is how the language strongly discourages nulls.  Even Anders went on video saying that he regretted making reference types nullable in C#.

Of course, there's no way to remove the nullable-by-default nature of reference types in D2, but a guy can dream. =]

On 12/10/13 9:40 AM, JR wrote:
> On Tuesday, 10 December 2013 at 17:28:26 UTC, Andrei Alexandrescu wrote:
>> We have only(x) (http://dlang.org/phobos/std_range.html#.only) to be a
>> collection of exactly one value, but not a type for "a value of type T
>> or nothing at all".
>
> Is this not what Nullable!T is?

Nullable is not a range.

Andrei

On 12/10/13 9:47 AM, Max Klyga wrote:
> On 2013-12-10 17:28:26 +0000, Andrei Alexandrescu said:
>
>> I talked to a programmer who knows Scala (among others) and he
>> mentioned the usefulness of the Option type - a zero or one element
>> collection (range in D terminology). Here's an article discussing it:
>> http://danielwestheide.com/blog/2012/12/19/the-neophytes-guide-to-scala-part-5-the-option-type.html
>>
>>
>> We have only(x) (http://dlang.org/phobos/std_range.html#.only) to be a
>> collection of exactly one value, but not a type for "a value of type T
>> or nothing at all". Should we follow Scala's example and add it?
>>
>>
>> Andrei
>
> Yes! Option is super useful. Use it all the time in Scala and Java (via
> Guava library).
> I suppose it will be defined as a range, so map will work on it?
> One of the useful things about options are the ability to chain them via
> flatMap, will this usecase be handled?

Yah, looks like flatMap is also useful (independently from Option). Should actually be flatMap!(R, uint depth = uint.max).

Andrei

Am 10.12.2013 18:54, schrieb Yota:
> On Tuesday, 10 December 2013 at 17:28:26 UTC, Andrei Alexandrescu wrote:
>> I talked to a programmer who knows Scala (among others) and he
>> mentioned the usefulness of the Option type - a zero or one element
>> collection (range in D terminology). Here's an article discussing it:
>> http://danielwestheide.com/blog/2012/12/19/the-neophytes-guide-to-scala-part-5-the-option-type.html
>>
>
> I really came to love Option when I was working in F#.  One of the
> things I love about F# is how the language strongly discourages nulls.
> Even Anders went on video saying that he regretted making reference
> types nullable in C#.
>
> Of course, there's no way to remove the nullable-by-default nature of
> reference types in D2, but a guy can dream. =]

It would probably break a lot of code, but the Eiffel, Kottlin's approach could be used.

In those languages, unless it is proven that a reference type is valid you cannot make use of its value.

Eiffel
http://docs.eiffel.com/sites/default/files/void-safe-eiffel.pdf

Kotlin
http://confluence.jetbrains.com/display/Kotlin/Null-safety

--
Paulo

On 12/10/13 10:21 AM, Paulo Pinto wrote:
> Am 10.12.2013 18:54, schrieb Yota:
>> On Tuesday, 10 December 2013 at 17:28:26 UTC, Andrei Alexandrescu wrote:
>>> I talked to a programmer who knows Scala (among others) and he
>>> mentioned the usefulness of the Option type - a zero or one element
>>> collection (range in D terminology). Here's an article discussing it:
>>> http://danielwestheide.com/blog/2012/12/19/the-neophytes-guide-to-scala-part-5-the-option-type.html
>>>
>>>
>>
>> I really came to love Option when I was working in F#.  One of the
>> things I love about F# is how the language strongly discourages nulls.
>> Even Anders went on video saying that he regretted making reference
>> types nullable in C#.
>>
>> Of course, there's no way to remove the nullable-by-default nature of
>> reference types in D2, but a guy can dream. =]
>
> It would probably break a lot of code, but the Eiffel, Kottlin's
> approach could be used.
>
> In those languages, unless it is proven that a reference type is valid
> you cannot make use of its value.
>
> Eiffel
> http://docs.eiffel.com/sites/default/files/void-safe-eiffel.pdf
>
> Kotlin
> http://confluence.jetbrains.com/display/Kotlin/Null-safety

Not that this is not worth discussing, but this is a different topic. I'm talking about ranges of zero or one elements.

Andrei

Andrei Alexandrescu:

>Should we follow Scala's example and add it?

Making an Option a D Range means it becomes a Mondad :-) There's then a need for more awareness of Option!T in map/filter/zip.

Related:
https://d.puremagic.com/issues/show_bug.cgi?id=9086

Bye,
bearophile

Am 10.12.2013 19:34, schrieb Andrei Alexandrescu:
> On 12/10/13 10:21 AM, Paulo Pinto wrote:
>> Am 10.12.2013 18:54, schrieb Yota:
>>> On Tuesday, 10 December 2013 at 17:28:26 UTC, Andrei Alexandrescu wrote:
>>>> I talked to a programmer who knows Scala (among others) and he
>>>> mentioned the usefulness of the Option type - a zero or one element
>>>> collection (range in D terminology). Here's an article discussing it:
>>>> http://danielwestheide.com/blog/2012/12/19/the-neophytes-guide-to-scala-part-5-the-option-type.html
>>>>
>>>>
>>>>
>>>
>>> I really came to love Option when I was working in F#.  One of the
>>> things I love about F# is how the language strongly discourages nulls.
>>> Even Anders went on video saying that he regretted making reference
>>> types nullable in C#.
>>>
>>> Of course, there's no way to remove the nullable-by-default nature of
>>> reference types in D2, but a guy can dream. =]
>>
>> It would probably break a lot of code, but the Eiffel, Kottlin's
>> approach could be used.
>>
>> In those languages, unless it is proven that a reference type is valid
>> you cannot make use of its value.
>>
>> Eiffel
>> http://docs.eiffel.com/sites/default/files/void-safe-eiffel.pdf
>>
>> Kotlin
>> http://confluence.jetbrains.com/display/Kotlin/Null-safety
>
> Not that this is not worth discussing, but this is a different topic.
> I'm talking about ranges of zero or one elements.
>
> Andrei
>
>

Ah ok