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bh=iChXM9jDvP9NZLqLPCWL/Z01MUkAV+3TR+PHiqkI134=; b=F3yPEv4vAVpLJDyCH9ZtOmM8nL5UjJZLdnoFGefN4v6yAzzhIwGQQx0Aw7XfyDCy8B70lzZJpvAabszJ8gJW/4FGhW3f8kFM3U2nnOdXJGgOCBELIlXgw21cKP6LfW+1zch4EPrrVvYKEh180uibPUXTvfRFZ1m3+FeBHyawOqo= Received: from DB5PR07MB0774.eurprd07.prod.outlook.com (10.161.195.22) by DB5PR07MB0776.eurprd07.prod.outlook.com (10.161.195.24) with Microsoft SMTP Server (TLS) id 15.1.365.19; Sat, 16 Jan 2016 12:56:29 +0000 Received: from DB5PR07MB0774.eurprd07.prod.outlook.com ([10.161.195.22]) by DB5PR07MB0774.eurprd07.prod.outlook.com ([10.161.195.22]) with mapi id 15.01.0365.023; Sat, 16 Jan 2016 12:56:29 +0000 From: John Burwell To: "dev@cloudstack.apache.org" Subject: Re: [DISCUSS][PROPOSE] use of optional instead of null Thread-Topic: [DISCUSS][PROPOSE] use of optional instead of null Thread-Index: AQHRIVNZgk4YknrZxUW/jRT1YPNxK57+d/iA Date: Sat, 16 Jan 2016 12:56:28 +0000 Message-ID: <6B16B76C-F2F6-4A07-A614-9FAC27CE5CB9@shapeblue.com> References: In-Reply-To: Accept-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.2104) authentication-results: spf=none (sender IP is ) smtp.mailfrom=john.burwell@shapeblue.com; 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boundary="----_=_NextPart_3eb0ec31-7614-4bd7-b23e-117f74272f15" ------_=_NextPart_3eb0ec31-7614-4bd7-b23e-117f74272f15 Content-Language: en-US Content-Type: text/plain; charset="utf-8" Content-ID: <3CD38F68C989D348A7B954F6D7C3DA89@eurprd07.prod.outlook.com> Content-Transfer-Encoding: quoted-printable Daan, I completely agree that returning null is bad. Not only does it yield a ton= of useless null checks, it creates leaky abstractions by spreading the han= dling of the missing case out beyond the boundary of the class/subsystem. As a big proponent of the Null Object Pattern [1], I really wanted to like = Optional. It is a great concept in functional languages. So, I tried using = it in three (3) different projects since 2011. In all three systems, I woul= d say that, at best, it was no better than returning null, and, in other ca= ses, worse. Since Optional.get throws an exception when the wrapped value i= s null, all optional accesses must be defensively checked so the code base = is littered with code like the following: if (value.isPresent()) { return value.get(); } So, basically, you end up replacing null checks and NPEs with isPresent che= cks and a Guava exception. As a bonus, when exceptions occurred in producti= on, we had explain the meaning of them. The quickest explanation =E2=80=94 = =E2=80=9CThey are the new NPE=E2=80=9D. For all new developers on the proje= cts, we had one more thing to explain to them which, again, was asking them= to do something differently with no added value. Based on these experience= s, I prefer null checks to optional. While it is more effort (i.e. more code), I have gone back to using the Nul= l Object Pattern implemented in this manner [2]. Not only does this approac= h avoid NPEs, it also explicitly defines the behavior for the missing case.= For more complex examples, it can be unit tested to ensure the missing cas= e behaves as expected. Thanks, -John [1]: https://en.wikipedia.org/wiki/Null_Object_pattern [2]: https://gist.github.com/jburwell/f5162ad2d2de32c842b3 > [ShapeBlue] John Burwell ShapeBlue d: +44 (20) 3603 0542 | s: +1 (571) 403-2411 e: john.burwell@shapeblue.com | t: | w: www.shapeblue.com a: 53 Chandos Place, Covent Garden London WC2N 4HS UK [cid:image6e2aab.png@2caaed35.4cb517dd] Shape Blue Ltd is a company incorporated in England & Wales. ShapeBlue Serv= ices India LLP is a company incorporated in India and is operated under lic= ense from Shape Blue Ltd. Shape Blue Brasil Consultoria Ltda is a company i= ncorporated in Brasil and is operated under license from Shape Blue Ltd. Sh= apeBlue SA Pty Ltd is a company registered by The Republic of South Africa = and is traded under license from Shape Blue Ltd. ShapeBlue is a registered = trademark. This email and any attachments to it may be confidential and are intended s= olely for the use of the individual to whom it is addressed. Any views or o= pinions expressed are solely those of the author and do not necessarily rep= resent those of Shape Blue Ltd or related companies. If you are not the int= ended recipient of this email, you must neither take any action based upon = its contents, nor copy or show it to anyone. Please contact the sender if y= ou believe you have received this email in error. On Nov 17, 2015, at 11:16 AM, Daan Hoogland wrote= : > > LS, > > As a spin off from a discussion in a PR where it is no longer relevant I > made another PR to show the principle of the use of Optionals[1] > > > Miguel from Schuberg Philis has been proposing this as replacement of the > bad practice of returning null in methods and I agree. In seldom cases it > might be more expedient to throw an exception, most notably when a null i= s > returned but no check against is done in the calling method. In those cas= es > throwing a CloudRuntimeException would be an easier way to go then the > pattern in this PR. This is a runtime exception however so maybe creating > an explicit one is more appropriate in those places. > > Anyway I want to propose to move to using the pattern from the PR from no= w > on. > > =E2=80=8B[1] https://github.com/apache/cloudstack/pull/1060=E2=80=8B > > =E2=80=8Bthoughts?=E2=80=8B > -- > Daan Find out more about ShapeBlue and our range of CloudStack related services: IaaS Cloud Design & Build | CSForge =E2=80=93 rapid IaaS deployment framework CloudStack Consulting | Cloud= Stack Software Engineering CloudStack Infrastructure Support | CloudStack Bootcamp Training Courses ------_=_NextPart_3eb0ec31-7614-4bd7-b23e-117f74272f15 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Daan,

I completely agree that returning null is bad. Not only does it yield a ton= of useless null checks, it creates leaky abstractions by spreading the han= dling of the missing case out beyond the boundary of the class/subsystem.
As a big proponent of the Null Object Pattern [1], I really wanted to like = Optional. It is a great concept in functional languages. So, I tried using = it in three (3) different projects since 2011. In all three systems, I woul= d say that, at best, it was no better than returning null, and, in other cases, worse. Since Optional.get throws= an exception when the wrapped value is null, all optional accesses must be= defensively checked so the code base is littered with code like the follow= ing:

if (value.isPresent()) {
return value.get();
}

So, basically, you end up replacing null checks and NPEs with isPresent che= cks and a Guava exception. As a bonus, when exceptions occurred in producti= on, we had explain the meaning of them. The quickest explanation =E2=80=94 = =E2=80=9CThey are the new NPE=E2=80=9D. For all new developers on the projects, we had one more thing to explain to them which, again, wa= s asking them to do something differently with no added value. Based on the= se experiences, I prefer null checks to optional.

While it is more effort (i.e. more code), I have gone back to using the Nul= l Object Pattern implemented in this manner [2]. Not only does this approac= h avoid NPEs, it also explicitly defines the behavior for the missing case.= For more complex examples, it can be unit tested to ensure the missing case behaves as expected.

Thanks,
-John

[1]: https://en.wikipedia.org/wiki/Null_Object_pattern
[2]: https://gist.github.com/jburwell/f5162ad2d2de32c842b3

>

3D"=
John Burwell
ShapeBlue
d:  +44 (20) = ;3603 0542 | s: +1 (571) 403-2411 
e:  john.burwell@shapeblue.com | t:   |  w:  www.shapeblue.com
a:  53 Chandos Place, Covent Garden London WC2N&n= bsp;4HS UK
3D"Twitter"3D""
Shape Blue Ltd is a company incorporated in England & Wales. ShapeBlue = Services India LLP is a company incorporated in India and is operated under= license from Shape Blue Ltd. Shape Blue Brasil Consultoria Ltda is a compa= ny incorporated in Brasil and is operated under license from Shape Blue Ltd. ShapeBlue SA Pty Ltd is a company regis= tered by The Republic of South Africa and is traded under license from Shap= e Blue Ltd. ShapeBlue is a registered trademark.
This email and any attachments to it may be confidential and are intended s= olely for the use of the individual to whom it is addressed. Any views or o= pinions expressed are solely those of the author and do not necessarily rep= resent those of Shape Blue Ltd or related companies. If you are not the intended recipient of this email, yo= u must neither take any action based upon its contents, nor copy or show it= to anyone. Please contact the sender if you believe you have received this= email in error.

On Nov 17, 2015, at 11:16 AM, Daan Hoogland <daan.hoogland@gmail.com>= wrote:
>
> LS,
>
> As a spin off from a discussion in a PR where it is no longer relevant= I
> made another PR to show the principle of the use of Optionals[1]
> <https://github.com/apache/cloudstack/pull/1060>
>
> Miguel from Schuberg Philis has been proposing this as replacement of = the
> bad practice of returning null in methods and I agree. In seldom cases= it
> might be more expedient to throw an exception, most notably when a nul= l is
> returned but no check against is done in the calling method. In those = cases
> throwing a CloudRuntimeException would be an easier way to go then the=
> pattern in this PR. This is a runtime exception however so maybe creat= ing
> an explicit one is more appropriate in those places.
>
> Anyway I want to propose to move to using the pattern from the PR from= now
> on.
>
> =E2=80=8B[1] https://github.com/apache/cloudstack/pull/1060=E2=80=8B >
> =E2=80=8Bthoughts?=E2=80=8B
> --
> Daan

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