recognise empty closure?

[OCsite <oc...@ocs.cz>]

Hi there,

is it possible to reliably recognise an empty closure, i.e., „{}“, programmatically? 

def foo(Closure bar) {
  if (?bar-is-empty?) throw new Exception('The closure cannot be empty!')
  else bar()
}
foo { println "ok" } // OK
foo { 1 } // OK
foo { } // throws

Thanks!
OC

Re: recognise empty closure?

[OCsite <oc...@ocs.cz>]

Hi there,

> On 17 Feb 2021, at 20:41, MG <mg...@arscreat.com> wrote:
> Is telling the user that the Closure cannot be empty the only application for this ?

Not quite; the particular application is a bit complicated and not worth to detail it here, but the gist is that my application offers a kind of API where in some cases an empty “onerror” closure bears a meaning “I don't care of errors if some happen”, and it would be nice if the core recognised that and did not log these errors either.

Nevertheless, it's not a particularly good API, and I guess I'll think of a way to improve it somehow, which would also get rid of a need for the empty-closure-based hack, too :)

> On 17/02/2021 19:51, Daniel Sun wrote:
>> Groovy does not support checking empty closure at runtime AFAIK, but we could check and set some property to closure while compiling, then get the property at runtime.

Probably not worth implementing Groovy-side; if I really need that, I can create an ASTT to do this at my side.

Thanks a lot!
OC


> If yes, given that a user can easily pass a non-empty but non-meaningful closure anyway I would question whether it is worth the effort.
> 
> Cheers,
> mg
> 
> PS: Also wondering whether we could achieve the same thing through the Closure return type, e.g.:
> @Test
> @Ignore
> void closureFooTest() {
>  println closureFoo {}
>  println closureFoo { "abc" }
> }
> 
> def closureFoo(Closure<String> cls) {
>  return "the string is: ${cls()}"
> }
> Should imho fail to compile, since an empty Closure should have return type void.
> Currently it does compile and run though (under 2.5.x) , even with @CompileStatic, since the empty closure implicitely returns null (imho one of the few bad design decisions in Groovy (whether in closures or somewhere else)), but at least IntelliJ marks it as invalid...
> 
> 
> 
> On 17/02/2021 19:51, Daniel Sun wrote:
>> Groovy does not support checking empty closure at runtime AFAIK, but we could check and set some property to closure while compiling, then get the property at runtime. It will be an new improvement, not sure if others like it or not.
>> 
>> Cheers,
>> Daniel Sun
>> 
>> On 2021/02/17 15:06:47, OCsite <oc...@ocs.cz> <ma...@ocs.cz> wrote: 
>>> Hi there,
>>> 
>>> is it possible to reliably recognise an empty closure, i.e., „{}“, programmatically? 
>>> 
>>> def foo(Closure bar) {
>>>   if (?bar-is-empty?) throw new Exception('The closure cannot be empty!')
>>>   else bar()
>>> }
>>> foo { println "ok" } // OK
>>> foo { 1 } // OK
>>> foo { } // throws
>>> 
>>> Thanks!
>>> OC
> 

Re: recognise empty closure?

[MG <mg...@arscreat.com>]

Is telling the user that the Closure cannot be empty the only 
application for this ? If yes, given that a user can easily pass a 
non-empty but non-meaningful closure anyway I would question whether it 
is worth the effort.

Cheers,
mg

PS: Also wondering whether we could achieve the same thing through the 
Closure return type, e.g.:

@Test @Ignore void closureFooTest() {
  println closureFoo {}
  println closureFoo{ "abc" } }

def closureFoo(Closure<String> cls) {
  return "the string is: ${cls()}" }

Should imho fail to compile, since an empty Closure should have return 
type void.
Currently it does compile and run though (under 2.5.x) , even with 
@CompileStatic, since the empty closure implicitely returns null (imho 
one of the few bad design decisions in Groovy (whether in closures or 
somewhere else)), but at least IntelliJ marks it as invalid...



On 17/02/2021 19:51, Daniel Sun wrote:
> Groovy does not support checking empty closure at runtime AFAIK, but we could check and set some property to closure while compiling, then get the property at runtime. It will be an new improvement, not sure if others like it or not.
>
> Cheers,
> Daniel Sun
>
> On 2021/02/17 15:06:47, OCsite <oc...@ocs.cz> wrote:
>> Hi there,
>>
>> is it possible to reliably recognise an empty closure, i.e., „{}“, programmatically?
>>
>> def foo(Closure bar) {
>>    if (?bar-is-empty?) throw new Exception('The closure cannot be empty!')
>>    else bar()
>> }
>> foo { println "ok" } // OK
>> foo { 1 } // OK
>> foo { } // throws
>>
>> Thanks!
>> OC

Re: recognise empty closure?

[Daniel Sun <su...@apache.org>]

Groovy does not support checking empty closure at runtime AFAIK, but we could check and set some property to closure while compiling, then get the property at runtime. It will be an new improvement, not sure if others like it or not.

Cheers,
Daniel Sun

On 2021/02/17 15:06:47, OCsite <oc...@ocs.cz> wrote: 
> Hi there,
> 
> is it possible to reliably recognise an empty closure, i.e., „{}“, programmatically? 
> 
> def foo(Closure bar) {
>   if (?bar-is-empty?) throw new Exception('The closure cannot be empty!')
>   else bar()
> }
> foo { println "ok" } // OK
> foo { 1 } // OK
> foo { } // throws
> 
> Thanks!
> OC