Re: DGM for first or default

[Mario Garcia]

Good point OC:

[0,'',[],[:]].find()?:'not quite what you wanted here'
[0,1,2].find()?:'nor in this case'

The more I think on this the more I think is an interesting topic. I fully
understand your frustration with first(), but apart from the example with
Cocoa you mentioned, looking in the JVM it turns out there're plenty of
examples of language collections behaving that way:

In scala the head of an empty list does throw an exception
---
scala> var empty = List[Int]()
empty: List[Int] = List()

scala> empty.head
java.util.NoSuchElementException: head of empty list
  at scala.collection.immutable.Nil$.head(List.scala:426)
  at scala.collection.immutable.Nil$.head(List.scala:423)
  ... 28 elided

scala>
-

and so does kotlin when calling to first()
--
Welcome to Kotlin version 1.2.71 (JRE 1.8.0_171-b11)
Type :help for help, :quit for quit
>>> val num: List = listOf()
>>> num.first()
java.util.NoSuchElementException: List is empty.
at
kotlin.collections.CollectionsKt___CollectionsKt.first(_Collections.kt:184)
>>>
-
in Kotlin they have firstOrNull(), but I haven't found any overloaded
function with a default value. They also have "find", but it's not possible
to call it without parameter

However Clojure returns null whether:

   - The first element was nil
   - The list was empty
   - Or the list was nil


user=> (def a nil)
#'user/a
user=> a
nil
user=> (first a)
nil
user=> (def a '(nil))
#'user/a
user=> a
(nil)
user=> (first a)
nil
user=> (def a '())
#'user/a
user=> a
()
user=> (first a)
nil
user=>
---

BTW I forgot to mention that Groovy 3 will have safe indexing meaning an
expression like the following:

   - will return the first element of a non empty list which I guess it
   will be the Kotlin firstOrNull() equivalent
   - or null if the list was null or empty

-
// trying to get first element from null list
nullList?[0] ==> null

// trying to get an inexistent element from a non empty list (but this is
not new, this is how a non empty list indexing works in Groovy)
nonNullList?[] => null
--

Outside the JVM, Haskell, when asking for the head of an empty list, throws
an exception (There is an explanation in stackoverflow which I'm afraid I
don't understand). So in the end Groovy's first() seems not to be the
exception among other modern languages out there.

Another point of view, could be thinking about returning null consistently.
Lets say a list returns null using first():

   - Does it mean the first element is a null value or is an empty list and
   that's why is giving me a null value ?
   - What if null is a valid value, with some meaning in my process ? With
   that context a method like firstOrNull() (even first(defaultValue) with a
   null list) could be considered ambiguous.

My guess is that in the case of languages throwing an exception using
first() on an empty list, when they designed the language collections they
didn't have any other way to express that kind of semantics. But this is
just a lucky guess. I'm probably wrong. I only can think of pattern
matching as a complete solution, where the terminal result in the case of
an empty or null list, is a default value different than any of the
elements of the expected result set ?

I apologize in advance for the lengthy e-mail, but it seemed interesting to
think why first() was designed like that, not only in Groovy, but in some
other languages as well.
Mario

El jue., 18 oct. 2018 a las 20:27, Milles, Eric (TR Technology & Ops) (<
eric.mil...@thomsonreuters.com>) escribió:

> I think first() exists so there is a semantic pair for functional
> programming: first()/head() and tail()  or init() and last()
>
> --
> *From:* ocs@ocs 
> *Sent:* Thursday, October 18, 2018 1:20 PM
> *To:* dev@groovy.apache.org
> *Subject:* Re: DGM for first or default
>
> Well I thought *first* is smart enough to return *null* for an empty
> list, same as my *firstObject* in Cocoa does. If it throws, what's on
> earth point of having the thing at all? In that case it can be replaced by
> *list[0]* without any drawback at all.
>
> All the best,
> OC
>
> On 18 Oct 2018, at 7:19 PM, Milles, Eric (TR Technology & Ops) <
> eric.mil...@thomsonreuters.com> wrote:
>
> "list?.first() ?: defaultValue" is not the equivalent.  If the collection
> is empty, first() throws an IndexOutOfBoundsException is thrown.  That's
> why I'm asking if there is a simple equivalent.  I suppose this is the
> equivalent now that I think about it:
>
> list ? list.first() : defaultValue
>
>
> --
> *From:* ocs@ocs 
> *Sent:* Thursday, October 18, 2018 12:07 PM
> *To:* dev@groovy.apache.org
> *Subject:* Re: DGM for first or default
>
> Myself, I am not a huge fan of adding not-often-needed functionalities
> (and actually would add almost none of those discussed lately);
> nevertheless...
>
> On 18 Oct 2018, at 

Re: DGM for first or default

[Milles, Eric (TR Technology & Ops)]

I think first() exists so there is a semantic pair for functional programming: 
first()/head() and tail()  or init() and last()


From: ocs@ocs 
Sent: Thursday, October 18, 2018 1:20 PM
To: dev@groovy.apache.org
Subject: Re: DGM for first or default

Well I thought first is smart enough to return null for an empty list, same as 
my firstObject in Cocoa does. If it throws, what's on earth point of having the 
thing at all? In that case it can be replaced by list[0] without any drawback 
at all.

All the best,
OC

On 18 Oct 2018, at 7:19 PM, Milles, Eric (TR Technology & Ops) 
mailto:eric.mil...@thomsonreuters.com>> wrote:

"list?.first() ?: defaultValue" is not the equivalent.  If the collection is 
empty, first() throws an IndexOutOfBoundsException is thrown.  That's why I'm 
asking if there is a simple equivalent.  I suppose this is the equivalent now 
that I think about it:

list ? list.first() : defaultValue



From: ocs@ocs mailto:o...@ocs.cz>>
Sent: Thursday, October 18, 2018 12:07 PM
To: dev@groovy.apache.org
Subject: Re: DGM for first or default

Myself, I am not a huge fan of adding not-often-needed functionalities (and 
actually would add almost none of those discussed lately); nevertheless...

On 18 Oct 2018, at 6:48 PM, Paolo Di Tommaso 
mailto:paolo.ditomm...@gmail.com>> wrote:

-1, it can be easily done as:
list.first() ?: defaultValue

... this won't work in case the first object is a Groovy False (e.g., an empty 
string, or a plethora of others).

All the best,
OC



p

On Thu, Oct 18, 2018 at 6:45 PM Daniel.Sun 
mailto:sun...@apache.org>> wrote:
+0 from me.
P.S. we should add similar DGM for `last` too?

Cheers,
Daniel.Sun




-
Daniel Sun
Apache Groovy committer
Blog: 
http://blog.sunlan.me
Twitter: @daniel_sun

--
Sent from: 
http://groovy.329449.n5.nabble.com/Groovy-Dev-f372993.html

Re: DGM for first or default

[ocs@ocs]

[0,'',[],[:]].find()?:'not quite what you wanted here'
[0,1,2].find()?:'nor in this case'

Actually, far as my experience can say, there's precisely one reason to have 
first/last, and that is that they won't throw, but return a null on an empty 
list. If they do not, there's no point in having those at all, for indices can 
be used instead just as well.

All the best,
OC

> On 18 Oct 2018, at 7:52 PM, Mario Garcia  wrote:
> 
> Eric you can use `find`:
> 
> list.find() ?: defaultValue
> 
> The method find with no arguments takes the first element, and if the 
> collection is empty or null it will return null and you won't get an 
> IndexOutOfBounds
> 
> Regards
> Mario
> 
> El jue., 18 oct. 2018 a las 19:32, Milles, Eric (TR Technology & Ops) 
> (mailto:eric.mil...@thomsonreuters.com>>) 
> escribió:
> Is it still valuable to have DGMs -- whether named "first()" or 
> "firstOrDefault()" or whatever?  Content assist does not propose "list ? 
> list.first() : defaultValue".  I suppose I'd need to create a code template 
> to get that proposal in the IDE.
> 
> Are there any other small idioms like this that anyone has added as a 
> template to improve the editing experience?
> From: Milles, Eric (TR Technology & Ops)
> Sent: Thursday, October 18, 2018 12:19:42 PM
> To: dev@groovy.apache.org 
> Subject: Re: DGM for first or default
>  
> "list?.first() ?: defaultValue" is not the equivalent.  If the collection is 
> empty, first() throws an IndexOutOfBoundsException is thrown.  That's why I'm 
> asking if there is a simple equivalent.  I suppose this is the equivalent now 
> that I think about it:
> 
> list ? list.first() : defaultValue
> 
> 
> From: ocs@ocs mailto:o...@ocs.cz>>
> Sent: Thursday, October 18, 2018 12:07 PM
> To: dev@groovy.apache.org 
> Subject: Re: DGM for first or default
>  
> Myself, I am not a huge fan of adding not-often-needed functionalities (and 
> actually would add almost none of those discussed lately); nevertheless...
> 
>> On 18 Oct 2018, at 6:48 PM, Paolo Di Tommaso > > wrote:
>> 
>> -1, it can be easily done as: 
>> list.first() ?: defaultValue
> 
> ... this won't work in case the first object is a Groovy False (e.g., an 
> empty string, or a plethora of others).
> 
> All the best,
> OC
> 
>> 
>> 
>> p
>> 
>> On Thu, Oct 18, 2018 at 6:45 PM Daniel.Sun > > wrote:
>> +0 from me.
>> P.S. we should add similar DGM for `last` too?
>> 
>> Cheers,
>> Daniel.Sun
>> 
>> 
>> 
>> 
>> -
>> Daniel Sun 
>> Apache Groovy committer 
>> Blog: http://blog.sunlan.me 
>> 
>>  
>> Twitter: @daniel_sun 
>> 
>> --
>> Sent from: http://groovy.329449.n5.nabble.com/Groovy-Dev-f372993.html 
>> 
> 

Re: DGM for first or default

[ocs@ocs]

Well I thought first is smart enough to return null for an empty list, same as 
my firstObject in Cocoa does. If it throws, what's on earth point of having the 
thing at all? In that case it can be replaced by list[0] without any drawback 
at all.

All the best,
OC

> On 18 Oct 2018, at 7:19 PM, Milles, Eric (TR Technology & Ops) 
>  wrote:
> 
> "list?.first() ?: defaultValue" is not the equivalent.  If the collection is 
> empty, first() throws an IndexOutOfBoundsException is thrown.  That's why I'm 
> asking if there is a simple equivalent.  I suppose this is the equivalent now 
> that I think about it:
> 
> list ? list.first() : defaultValue
> 
> 
> From: ocs@ocs mailto:o...@ocs.cz>>
> Sent: Thursday, October 18, 2018 12:07 PM
> To: dev@groovy.apache.org 
> Subject: Re: DGM for first or default
>  
> Myself, I am not a huge fan of adding not-often-needed functionalities (and 
> actually would add almost none of those discussed lately); nevertheless...
> 
>> On 18 Oct 2018, at 6:48 PM, Paolo Di Tommaso > > wrote:
>> 
>> -1, it can be easily done as: 
>> list.first() ?: defaultValue
> 
> ... this won't work in case the first object is a Groovy False (e.g., an 
> empty string, or a plethora of others).
> 
> All the best,
> OC
> 
>> 
>> 
>> p
>> 
>> On Thu, Oct 18, 2018 at 6:45 PM Daniel.Sun > > wrote:
>> +0 from me.
>> P.S. we should add similar DGM for `last` too?
>> 
>> Cheers,
>> Daniel.Sun
>> 
>> 
>> 
>> 
>> -
>> Daniel Sun 
>> Apache Groovy committer 
>> Blog: http://blog.sunlan.me 
>> 
>>  
>> Twitter: @daniel_sun 
>> 
>> --
>> Sent from: http://groovy.329449.n5.nabble.com/Groovy-Dev-f372993.html 
>> 

Re: DGM for first or default

[Mario Garcia]

Eric you can use `find`:

list.find() ?: defaultValue

The method find with no arguments takes the first element, and if the
collection is empty or null it will return null and you won't get an
IndexOutOfBounds

Regards
Mario

El jue., 18 oct. 2018 a las 19:32, Milles, Eric (TR Technology & Ops) (<
eric.mil...@thomsonreuters.com>) escribió:

> Is it still valuable to have DGMs -- whether named "first()" or
> "firstOrDefault()" or whatever?  Content assist does not propose "list ?
> list.first() : defaultValue".  I suppose I'd need to create a code template
> to get that proposal in the IDE.
>
>
> Are there any other small idioms like this that anyone has added as a
> template to improve the editing experience?
> --
> *From:* Milles, Eric (TR Technology & Ops)
> *Sent:* Thursday, October 18, 2018 12:19:42 PM
> *To:* dev@groovy.apache.org
> *Subject:* Re: DGM for first or default
>
>
> "list?.first() ?: defaultValue" is not the equivalent.  If the collection
> is empty, first() throws an IndexOutOfBoundsException is thrown.  That's
> why I'm asking if there is a simple equivalent.  I suppose this is the
> equivalent now that I think about it:
>
>
> list ? list.first() : defaultValue
>
>
> --
> *From:* ocs@ocs 
> *Sent:* Thursday, October 18, 2018 12:07 PM
> *To:* dev@groovy.apache.org
> *Subject:* Re: DGM for first or default
>
> Myself, I am not a huge fan of adding not-often-needed functionalities
> (and actually would add almost none of those discussed lately);
> nevertheless...
>
> On 18 Oct 2018, at 6:48 PM, Paolo Di Tommaso 
> wrote:
>
> -1, it can be easily done as:
> list.first() ?: defaultValue
>
>
> ... this won't work in case the first object is a Groovy False (e.g., an
> empty string, or a plethora of others).
>
> All the best,
> OC
>
>
>
> p
>
> On Thu, Oct 18, 2018 at 6:45 PM Daniel.Sun  wrote:
>
> +0 from me.
> P.S. we should add similar DGM for `last` too?
>
> Cheers,
> Daniel.Sun
>
>
>
>
> -
> Daniel Sun
> Apache Groovy committer
> Blog: http://blog.sunlan.me
> 
> Twitter: @daniel_sun
>
> --
> Sent from: http://groovy.329449.n5.nabble.com/Groovy-Dev-f372993.html
> 
>
>
>

Re: DGM for first or default

[Milles, Eric (TR Technology & Ops)]

Is it still valuable to have DGMs -- whether named "first()" or 
"firstOrDefault()" or whatever?  Content assist does not propose "list ? 
list.first() : defaultValue".  I suppose I'd need to create a code template to 
get that proposal in the IDE.


Are there any other small idioms like this that anyone has added as a template 
to improve the editing experience?


From: Milles, Eric (TR Technology & Ops)
Sent: Thursday, October 18, 2018 12:19:42 PM
To: dev@groovy.apache.org
Subject: Re: DGM for first or default


"list?.first() ?: defaultValue" is not the equivalent.  If the collection is 
empty, first() throws an IndexOutOfBoundsException is thrown.  That's why I'm 
asking if there is a simple equivalent.  I suppose this is the equivalent now 
that I think about it:


list ? list.first() : defaultValue



From: ocs@ocs 
Sent: Thursday, October 18, 2018 12:07 PM
To: dev@groovy.apache.org
Subject: Re: DGM for first or default

Myself, I am not a huge fan of adding not-often-needed functionalities (and 
actually would add almost none of those discussed lately); nevertheless...

On 18 Oct 2018, at 6:48 PM, Paolo Di Tommaso 
mailto:paolo.ditomm...@gmail.com>> wrote:

-1, it can be easily done as:
list.first() ?: defaultValue

... this won't work in case the first object is a Groovy False (e.g., an empty 
string, or a plethora of others).

All the best,
OC



p

On Thu, Oct 18, 2018 at 6:45 PM Daniel.Sun 
mailto:sun...@apache.org>> wrote:
+0 from me.
P.S. we should add similar DGM for `last` too?

Cheers,
Daniel.Sun




-
Daniel Sun
Apache Groovy committer
Blog: 
http://blog.sunlan.me
Twitter: @daniel_sun

--
Sent from: 
http://groovy.329449.n5.nabble.com/Groovy-Dev-f372993.html

Re: DGM for first or default

[Milles, Eric (TR Technology & Ops)]

"list?.first() ?: defaultValue" is not the equivalent.  If the collection is 
empty, first() throws an IndexOutOfBoundsException is thrown.  That's why I'm 
asking if there is a simple equivalent.  I suppose this is the equivalent now 
that I think about it:


list ? list.first() : defaultValue



From: ocs@ocs 
Sent: Thursday, October 18, 2018 12:07 PM
To: dev@groovy.apache.org
Subject: Re: DGM for first or default

Myself, I am not a huge fan of adding not-often-needed functionalities (and 
actually would add almost none of those discussed lately); nevertheless...

On 18 Oct 2018, at 6:48 PM, Paolo Di Tommaso 
mailto:paolo.ditomm...@gmail.com>> wrote:

-1, it can be easily done as:
list.first() ?: defaultValue

... this won't work in case the first object is a Groovy False (e.g., an empty 
string, or a plethora of others).

All the best,
OC



p

On Thu, Oct 18, 2018 at 6:45 PM Daniel.Sun 
mailto:sun...@apache.org>> wrote:
+0 from me.
P.S. we should add similar DGM for `last` too?

Cheers,
Daniel.Sun




-
Daniel Sun
Apache Groovy committer
Blog: 
http://blog.sunlan.me
Twitter: @daniel_sun

--
Sent from: 
http://groovy.329449.n5.nabble.com/Groovy-Dev-f372993.html

Re: DGM for first or default

[Paolo Di Tommaso]

ouch.. true! if so:

list ? list.first() : defaultValue


p








On Thu, Oct 18, 2018 at 7:07 PM ocs@ocs  wrote:

> Myself, I am not a huge fan of adding not-often-needed functionalities
> (and actually would add almost none of those discussed lately);
> nevertheless...
>
> On 18 Oct 2018, at 6:48 PM, Paolo Di Tommaso 
> wrote:
>
> -1, it can be easily done as:
> list.first() ?: defaultValue
>
>
> ... this won't work in case the first object is a Groovy False (e.g., an
> empty string, or a plethora of others).
>
> All the best,
> OC
>
>
>
> p
>
> On Thu, Oct 18, 2018 at 6:45 PM Daniel.Sun  wrote:
>
>> +0 from me.
>> P.S. we should add similar DGM for `last` too?
>>
>> Cheers,
>> Daniel.Sun
>>
>>
>>
>>
>> -
>> Daniel Sun
>> Apache Groovy committer
>> Blog: http://blog.sunlan.me
>> Twitter: @daniel_sun
>>
>> --
>> Sent from: http://groovy.329449.n5.nabble.com/Groovy-Dev-f372993.html
>>
>
>

Re: DGM for first or default

[ocs@ocs]

P.S. Oh, and when I am writing anyway — please, do not abuse the “overloaded” 
methods which differ just by their argument lists (myself, I consider them 
always at best suspicious; mostly plain wrong). Instead of the suggestion 
below, if something like that is accepted, it would be much better to change 
the method name appropriately (say, e.g., firstWithDefault, firstWithSupplier). 
Or perhaps named arguments might be (consistently!) used for these things 
(e.g., “first(default:value)” or “first(supplier:value)”).

Consider e.g., an array of closures, of which one would want to get the first 
one with a default closure... with the definitions suggested below that's going 
to be fun!

All the best,
OC

> On 18 Oct 2018, at 5:39 PM, Milles, Eric (TR Technology & Ops) 
>  wrote:
> 
> I see there are the following DGMs for getting first element of a 
> "collection":
>   static  T first(T[] self)
>   static  T first(List self)
>   static  T first(Iterable self)
> 
> Is there a simple sequence for getting the first element or a default value 
> if the "collection" is empty?  If not, may I propose the addition of the 
> following DGMs:
>   static  T first(T[] self, T defaultValue)
>   static  T first(List self, T defaultValue)
>   static  T first(Iterable self, T defaultValue)
>   static  T first(T[] self, Closure defaultSupplier)
>   static  T first(List self, Closure defaultSupplier)
>   static  T first(Iterable self, Closure defaultSupplier)
> 
> 
> Eric M.

Re: DGM for first or default

[ocs@ocs]

Myself, I am not a huge fan of adding not-often-needed functionalities (and 
actually would add almost none of those discussed lately); nevertheless...

> On 18 Oct 2018, at 6:48 PM, Paolo Di Tommaso  
> wrote:
> 
> -1, it can be easily done as: 
> list.first() ?: defaultValue

... this won't work in case the first object is a Groovy False (e.g., an empty 
string, or a plethora of others).

All the best,
OC

> 
> 
> p
> 
> On Thu, Oct 18, 2018 at 6:45 PM Daniel.Sun  > wrote:
> +0 from me.
> P.S. we should add similar DGM for `last` too?
> 
> Cheers,
> Daniel.Sun
> 
> 
> 
> 
> -
> Daniel Sun 
> Apache Groovy committer 
> Blog: http://blog.sunlan.me  
> Twitter: @daniel_sun 
> 
> --
> Sent from: http://groovy.329449.n5.nabble.com/Groovy-Dev-f372993.html 
> 

Re: DGM for first or default

[Mauro Molinari]

Isn't it equivalent to something like this?

|def elem = collection?.first()?: defaultValue||
||def elem = collection?.first()?: defaultSupplier()||
|
Mauro

Il 18/10/2018 17:39, Milles, Eric (TR Technology & Ops) ha scritto:


I see there are the following DGMs for getting first element of 
a "collection":


  staticTfirst(T[] self)

  staticTfirst(Listself)

staticTfirst(Iterableself)


*Is there a simple sequence for getting the first element or a default 
value if the "collection" is empty?*  If not, may I propose the 
addition of the following DGMs:


  staticTfirst(T[] self, TdefaultValue)

  staticTfirst(Listself, TdefaultValue)

  staticTfirst(Iterableself, TdefaultValue)

  staticTfirst(T[] self, Closure defaultSupplier)
staticTfirst(Listself, Closure defaultSupplier)

  staticTfirst(Iterableself, Closure defaultSupplier)



Eric M.

Re: DGM for first or default

[Paolo Di Tommaso]

-1, it can be easily done as:

list.first() ?: defaultValue


p

On Thu, Oct 18, 2018 at 6:45 PM Daniel.Sun  wrote:

> +0 from me.
> P.S. we should add similar DGM for `last` too?
>
> Cheers,
> Daniel.Sun
>
>
>
>
> -
> Daniel Sun
> Apache Groovy committer
> Blog: http://blog.sunlan.me
> Twitter: @daniel_sun
>
> --
> Sent from: http://groovy.329449.n5.nabble.com/Groovy-Dev-f372993.html
>

Re: DGM for first or default

[Daniel.Sun]

+0 from me.
P.S. we should add similar DGM for `last` too?

Cheers,
Daniel.Sun




-
Daniel Sun 
Apache Groovy committer 
Blog: http://blog.sunlan.me 
Twitter: @daniel_sun 

--
Sent from: http://groovy.329449.n5.nabble.com/Groovy-Dev-f372993.html

DGM for first or default

[Milles, Eric (TR Technology & Ops)]

I see there are the following DGMs for getting first element of a "collection":

  static  T first(T[] self)

  static  T first(List self)

  static  T first(Iterable self)


Is there a simple sequence for getting the first element or a default value if 
the "collection" is empty?  If not, may I propose the addition of the following 
DGMs:

  static  T first(T[] self, T defaultValue)

  static  T first(List self, T defaultValue)

  static  T first(Iterable self, T defaultValue)

  static  T first(T[] self, Closure defaultSupplier)
  static  T first(List self, Closure defaultSupplier)

  static  T first(Iterable self, Closure defaultSupplier)



Eric M.