Spread-dot and collect() question

[Marc Palmer Local]

Hi,

I read from the groovy docs (http://groovy.codehaus.org/Operators#Operators-SpreadOperator%28.%29 
):

"The spread operator may be used a method call or property access, and  
returns a list of the items returned from each child call. So you may  
effectively override the spread operator by implementing a custom  
collect method."

I tried overriding the collect method on my collection, but it is  
never called:

class ExpressionNodeList extends ArrayList {
     ExpressionNodeList(List l) {
         super(l)
     }

     List collect(Closure c) {
         println "In our custom collect"
        return new ExpressionNodeList( xxxx.collect(c) )
     }
}


When I do something like:

assertTrue root.Chapters instanceof ExpressionNodeList
assertTrue root.Chapters*.Chapter instanceof ExpressionNodeList

This second line fails, and I get no printlns. The docs imply that  
root.Chapters.collect { it.Chapter } will be called, but it seems not.

What's wrong - the impl or the docs... or my brain?

FYI - Groovy 1.6.4

Thanks
Marc


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[Marc Palmer Local]

On 3 Nov 2009, at 12:19, Marc Palmer wrote:

> Hi,
>
> I read from the groovy docs (http://groovy.codehaus.org/Operators#Operators-SpreadOperator%28.%29 
> ):
>
> "The spread operator may be used a method call or property access,  
> and returns a list of the items returned from each child call. So  
> you may effectively override the spread operator by implementing a  
> custom collect method."
>
> I tried overriding the collect method on my collection, but it is  
> never called:

Here's a concise complete example:

class CustomList extends ArrayList {
     List collect(Closure c) {
         println "Custom collect!"
         return new LinkedList( this.collect(c) )
     }
}

def x = new CustomList()
x << [name:'A']
x << [name:'B']

assert x instanceof CustomList
assert x.size() == 2
assert x.name == ['A', 'B']
assert x*.name instanceof LinkedList

No printlns, and the last assert fails.

Where is the problem?

Thanks
Marc
~ ~ ~
Marc Palmer
Blog         > http://www.anyware.co.uk
Twitter      > http://twitter.com/wangjammer5
Grails Rocks > http://www.grailsrocks.com







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[Robert Fischer]

The docs are a lie[1].  I've never been able to overload *., either.

[1] http://www.urbandictionary.com/define.php?term=the+cake+is+a+lie

~~ Robert Fischer, Smokejumper IT Consulting.
Enfranchised Mind Blog http://EnfranchisedMind.com/blog

Grails Expert Retainer Services
http://smokejumperit.com/grails-retainer/


Marc Palmer wrote:

>
> On 3 Nov 2009, at 12:19, Marc Palmer wrote:
>
>> Hi,
>>
>> I read from the groovy docs
>> (http://groovy.codehaus.org/Operators#Operators-SpreadOperator%28.%29):
>>
>> "The spread operator may be used a method call or property access, and
>> returns a list of the items returned from each child call. So you may
>> effectively override the spread operator by implementing a custom
>> collect method."
>>
>> I tried overriding the collect method on my collection, but it is
>> never called:
>
> Here's a concise complete example:
>
> class CustomList extends ArrayList {
>     List collect(Closure c) {
>         println "Custom collect!"
>         return new LinkedList( this.collect(c) )
>     }
> }
>
> def x = new CustomList()
> x << [name:'A']
> x << [name:'B']
>
> assert x instanceof CustomList
> assert x.size() == 2
> assert x.name == ['A', 'B']
> assert x*.name instanceof LinkedList
>
> No printlns, and the last assert fails.
>
> Where is the problem?
>
> Thanks
> Marc
> ~ ~ ~
> Marc Palmer
> Blog         > http://www.anyware.co.uk
> Twitter      > http://twitter.com/wangjammer5
> Grails Rocks > http://www.grailsrocks.com
>
>
>
>
>
>
>
> ---------------------------------------------------------------------
> To unsubscribe from this list, please visit:
>
>    http://xircles.codehaus.org/manage_email
>
>
>

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[Paul King]

Yes, I suspect that the docs are out of date. The code implementing
the spreading is very similar to the code implementing collect but
currently collect isn't explicitly called. Perhaps it once did
call collect and was changed to tweak some of the edge cases.
A browse through svn history may shed some light.
Perhaps it could be made to call collect again - it would need
some further investigation - if you have what you believe to be
a very good use case I would create a feature enhancement Jira.
We should have a doco fix Jira as well in the meantime.

You could override iterator() instead for some scenarios.

Paul.

Robert Fischer wrote:

> The docs are a lie[1].  I've never been able to overload *., either.
>
> [1] http://www.urbandictionary.com/define.php?term=the+cake+is+a+lie
>
> ~~ Robert Fischer, Smokejumper IT Consulting.
> Enfranchised Mind Blog http://EnfranchisedMind.com/blog
>
> Grails Expert Retainer Services
> http://smokejumperit.com/grails-retainer/
>
>
> Marc Palmer wrote:
>>
>> On 3 Nov 2009, at 12:19, Marc Palmer wrote:
>>
>>> Hi,
>>>
>>> I read from the groovy docs
>>> (http://groovy.codehaus.org/Operators#Operators-SpreadOperator%28.%29):
>>>
>>> "The spread operator may be used a method call or property access,
>>> and returns a list of the items returned from each child call. So you
>>> may effectively override the spread operator by implementing a custom
>>> collect method."
>>>
>>> I tried overriding the collect method on my collection, but it is
>>> never called:
>>
>> Here's a concise complete example:
>>
>> class CustomList extends ArrayList {
>>     List collect(Closure c) {
>>         println "Custom collect!"
>>         return new LinkedList( this.collect(c) )
>>     }
>> }
>>
>> def x = new CustomList()
>> x << [name:'A']
>> x << [name:'B']
>>
>> assert x instanceof CustomList
>> assert x.size() == 2
>> assert x.name == ['A', 'B']
>> assert x*.name instanceof LinkedList
>>
>> No printlns, and the last assert fails.
>>
>> Where is the problem?
>>
>> Thanks
>> Marc
>> ~ ~ ~
>> Marc Palmer
>> Blog         > http://www.anyware.co.uk
>> Twitter      > http://twitter.com/wangjammer5
>> Grails Rocks > http://www.grailsrocks.com
>>
>>
>>
>>
>>
>>
>>
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>> To unsubscribe from this list, please visit:
>>
>>    http://xircles.codehaus.org/manage_email
>>
>>
>>
>
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> To unsubscribe from this list, please visit:
>
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>
>
>
>

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