Oops, there is a last minute cut/paste error in my example script. It should
read:
a = { x ->
println x.class
println x
x.write('foo')
return 'bar'
}
assert "no argument ${a}" == "no argument foo"
and it will print:
class java.io.StringWriter
no argument
Keith
> On Jan 21, 2017, at 2:37 PM, Suderman Keith <[email protected]> wrote:
>
> This took me awhile to wrap my head around this as well. Keep in mind what
> Guillaume said, the object passed to the closure is a writer. This example
> should hopefully make it clearer what is going on:
>
> a = {
> println x.class
> x -> println x
> x.write('foo')
> return 'bar'
> }
> assert "no argument ${a}" == "no argument foo"
>
> This will print "class java.io.StringWriter" to System.out
>
> Since the parameter passed to the closure is a StringWriter 'println x' will
> cause Groovy to call toString() on the writer, which already contains the
> string "no argument ". The string 'foo' is then appended to the writer so
> the GString finally resolves to "no argument foo". Notice the return value
> from the closure is ignored.
>
> Hope this helps,
> Keith
>
>
>
>> On Jan 21, 2017, at 12:54 PM, Anthony Hepple <[email protected]>
>> wrote:
>>
>> Hi Yang
>>
>> I too am confused. The following code better describes my confusion:
>>
>> a = {x -> println x}
>> assert "no argument ${a}" == "no argument "
>>
>> So far so good, but why does this have the side effect of printing "no
>> argument" to standard out? As you say, the closure, a, appears to
>> magically capture the string "no argument".
>>
>> Perhaps if someone could explain this they would help us both?
>>
>> Thanks
>> Anthony
>>
>> On 21 January 2017 at 16:19, Guillaume Laforge <[email protected]> wrote:
>>> x doesn't capture the value "a".
>>> Your GString contains a "a", and when you call a() you pass the string "a"
>>> to it.
>>> So the a() call return "a", and you print "a", so you see the output as well
>>> as the println of "a", thus two "a"'s.
>>>
>>> Not sure how you came with that code. It's pretty confusing.
>>> Normally, if you use a one-arg closure inside a GString, the parameter of
>>> the closure is actually a writer against which you can write. You're not
>>> supposed to print from there or have side effects.
>>>
>>> What are you trying to achieve here?
>>>
>>> Guillaume
>>>
>>> On Sat, Jan 21, 2017 at 4:46 AM, Yang Yang <[email protected]> wrote:
>>>>
>>>> Sorry, after reading that part of documentation I still feel a bit
>>>> confused.
>>>>
>>>> groovy:000> "a${x->println x}"
>>>> a
>>>> a
>>>> ===> a
>>>> groovy:000> a = {x->println x}
>>>> ===> groovysh_evaluate$_run_closure1@737a135b
>>>> groovy:000> a("a${x->println x}")
>>>> a
>>>> a
>>>> ===> null
>>>>
>>>> Say "a${a}" will be expanded as "a${x->println x}" and I don't understand
>>>> why x captured the value "a" ?
>>>>
>>>> "a${x->println x}" will output "a" because ${x->println x} will be lazy
>>>> evaluated. Then the result "a" is magically captured by the closure
>>>> {x->println x} and it print another "a". But if it like so then the first
>>>> return ===> should be null.
>>>>
>>>>
>>>>
>>>> On 20 Jan 2017, at 16:49, Guillaume Laforge <[email protected]> wrote:
>>>>
>>>> Hi Yang,
>>>>
>>>> Interpolated values in a GString that are closures are executed.
>>>> Have a look at the documentation which shows some examples of this:
>>>>
>>>> http://groovy-lang.org/syntax.html#_special_case_of_interpolating_closure_expressions
>>>>
>>>> Guillaume
>>>>
>>>>
>>>> On Fri, Jan 20, 2017 at 8:22 AM, Yang Yang <[email protected]> wrote:
>>>>>
>>>>> Script:
>>>>> a = {x -> println x}
>>>>> a("a${a}")
>>>>>
>>>>> Output:
>>>>> a
>>>>> a
>>>>>
>>>>> Why?
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Guillaume Laforge
>>>> Apache Groovy committer & PMC Vice-President
>>>> Developer Advocate @ Google Cloud Platform
>>>>
>>>> Blog: http://glaforge.appspot.com/
>>>> Social: @glaforge / Google+
>>>>
>>>>
>>>
>>>
>>>
>>> --
>>> Guillaume Laforge
>>> Apache Groovy committer & PMC Vice-President
>>> Developer Advocate @ Google Cloud Platform
>>>
>>> Blog: http://glaforge.appspot.com/
>>> Social: @glaforge / Google+
>>
>>
>>
>> --
>> Anthony Hepple
>> 01704 227828 / 07931 504049
>> http://www.dhdevelopment.co.uk
