On Sun, 2014-10-05 at 10:29 +0200, Johan Brichau wrote:
Itâs true that when you do a lot of cross-dialect development, such a method is often what you desire. However, I think itâs better to do feature detection instead of dialect detection. So, something like:
((Smalltalk includesKey: #CharacterWriteStream) ifTrue:[ stream := CharacterWriteStream on: (String new: 10) ] ifFalse:[ stream := WriteStream on: (String new: 10) ]
Right, in this example it could eventually work. Another concrete example I bumped just yesterday. The "feature testing" code would look like ((Character respondsTo: #to:) and:[($a to: $z) isKindOf: Interval]) ifTrue:[ ... ] ifFalse:[ ... ]. (true, in this very case you may be able to get around using different method, but you get the point, no?) Some time ago Hilaire posted a very nice, 15 lines long code that does reliable "feature detection" whether the system is Pharo 2.0 or 3.0 (or similar, I don't remember exactly). Is the interval testing code above more robust? Perhaps. Is it more readable, more intention revelaling? I doubt it. While I can agree that feature testing is is better, however, in my experience it is very tricky if the code does not provide support for such tests.
And yes: use Grease where applicable. We try to maintain Grease across Pharo, Squeak and Gemstone. I also think itâs actively ported to VA.
That's great. But having such dependency is exactly what I, and not only me, don't want if it would be for only one or two methods. The aim is to provide a simple solution for simple cases, not a silver bullet. Jan
cheers Johan
On 05 Oct 2014, at 09:00, stepharo <stepharo@free.fr> wrote:
Hi jan
Thanks for the proposal. I thought about it and I'm against because it goes again the idea of dispatch. I prefer to have a class and some dispatch. Seaside with Grease is the way to go from my perspective. Finally I do not want such methods in the systems because I spent my time removing isXXXX because of bad design. Let us see what other people think.
Stef
On 4/10/14 22:14, Jan Vrany wrote:
Hi guys,
I've just opened:
https://pharo.fogbugz.com/f/cases/14160/Introduce-isXXX-dialect-testing-meth...
Introduce isXXX (isPharo, isVisualWorks, ...) dialect testing methods to SmalltalkImage to ease multi-dialect development.
RATIONALE:
Commonly used approach to solve differences among dialect is to use a sort of platform object and dispatch there for troublesome operations that has to be specialized. This platform object is usually in platform specific package. Other option is to load some library like Grease or Sport.
The problem of the first approach is that brings to much (unnecessary) burden when used for two, three things. The amount of of the code and management is way to bigger then the amount of the code that has to be specialized. Loading Grease/Sport on the other hand introduces a dependency on an external package - not worth of for two or three things.
The proposed dialect testing messages would allow for simple, #ifdef-like idiom like:
| stream | ... ((Smalltalk respondsTo: #isSomeCoolDialect) and:[Smalltalk isSomeCoolDialect]) ifTrue:[ stream := CharacterWriteStream on: (String new: 10) ] ifFalse:[ stream := WriteStream on: (String new: 10) ]
The #respondsTo: check, while not nice, is required as at the moment not all dialects could be trusted to have these testing messages.
Putting these methods may not stick with Pharo standard (whatever it is), but Smalltalk global is probably one of the very few that are present in pretty much every Smalltalk implementation. Other option would be to place them to the class side of an Object (which is amost certainly present everywhere), however
Smalltalk isPharo
reads better than
Object isPharo.
Best, Jan