Re: `new Foo` vs `new Foo()`

[caution, some nit-picking ahead]

Well, that depends: object allocation can cause widely visible effects like GC pauses and simple constructor execution in many cases entails memory barriers (i.e. visible concurrency and latency effects). I agree that such effects usually are ubiquitous and therefore not much can be gained from explicitly tracking them in normal code bases, but Scala can also be used in a fashion that avoids allocation in substantial parts of the program.

Regards,

Roland

> 14 jul 2015 kl. 12:34 skrev Jon Pretty <[email protected]>:
> 
> Yes, in hindsight, it's not particularly *useful* to consider instantiation as a side-effect in Scala... ;)
> 
> Cheers,
> Jon
> 
> On 14 July 2015 at 02:05, Haoyi Li <[email protected] <mailto:[email protected]>> wrote:
> > I didn't mean to imply allocation is side-effecting. I meant the side effect of the initializer in your case class would be invoked every time you instantiate it, whereas the effect in an object's body occur at most once.
> 
> Oh ok. I thought you were agreeing with jon, who said instantiating a new instance of a class was a side effect (???)
> 
> On Mon, Jul 13, 2015 at 5:02 PM, Adriaan Moors <[email protected] <mailto:[email protected]>> wrote:
> I didn't mean to imply allocation is side-effecting. I meant the side effect of the initializer in your case class would be invoked every time you instantiate it, whereas the effect in an object's body occur at most once.
> 
> On Mon, Jul 13, 2015 at 4:05 PM, Haoyi Li <[email protected] <mailto:[email protected]>> wrote:
> > That's the reasoning for case classes, I guess, since a side-effect-free case class should be a case object.
> 
> This doesn't make sense to me. Since when was object allocation considered side effecting? When people say "avoid side effects", they usually mean you should allocate *more* objects, not less! Is CaseClass#copy just as side-effecting as mutating vars?
> 
> On Mon, Jul 13, 2015 at 2:13 PM, Adriaan Moors <[email protected] <mailto:[email protected]>> wrote:
> If we apply the same rule as for methods, you should not add parens unless your constructor is side-effecting (which is probably not a great idea in itself).
> That's the reasoning for case classes, I guess, since a side-effect-free case class should be a case object.
> 
> I tend to leave off the empty parens. Their presence should imply potential side-effects.
> 
> On Mon, Jul 13, 2015 at 1:28 PM, Jon Pretty <[email protected] <mailto:[email protected]>> wrote:
> I tend to include the parentheses for a couple of reasons: firstly because case classes require the parens, and by association I justify that classes should too, and secondly because instantiating a new instance of a class is side-effecting, so the "method" which does that (i.e. the constructor) should look like a side-effecting method.
> 
> Additionally, for some reason, I prefer to write `new Foo().bar` rather than `(new Foo).bar`. I think the reason is that I have a slight discomfort at starting an expression with an opening parenthesis, and I've taught myself to give the `new` in `new Foo().bar` higher precedence than the `.`, even though this is counterintuitive to other parsing rules.
> 
> Jon​
> 
> On 13 July 2015 at 21:20, Rex Kerr <[email protected] <mailto:[email protected]>> wrote:
> That's the convention I use.  I've seen both with and without parens in e.g. the Scala library code base.
> 
>   --Rex
> 
> On Mon, Jul 13, 2015 at 12:06 PM, Seth Tisue <[email protected] <mailto:[email protected]>> wrote:
> Is there consensus on this? Not sure whether to merge.
> 
> https://github.com/scala/scala.github.com/pull/344 <https://github.com/scala/scala.github.com/pull/344>
> 
> Seth
> 
> 
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Dr. Roland Kuhn
Akka Tech Lead
Typesafe <http://typesafe.com/> – Reactive apps on the JVM.
twitter: @rolandkuhn
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