[squeak-dev] What are the current use cases for traits? (was: The Inbox: TraitsTests-pre.19.mcz)

Jakob Reschke forums.jakob at resfarm.de
Fri May 3 23:47:39 UTC 2019

I have another one:

For several test cases I have to suppress the display of progress
(otherwise the tests would run much slower). To do that, I override
performTest to catch the relevant exceptions/notifications and mute them. I
need that in multiple test case classes, but I do not want to provide the
progress suppressing with an abstract test superclass. So I created a trait
that contains this performTest override. Test cases that need the progress
muted can mix that in by using the trait.

Why don't I want the abstract superclass? Because I have two more such
traits for test cases: one that provides additional assert methods for a
certain type of object, and one that provides a method for suppressing
change notifications so the changes file is not cluttered that much when
the tests run. As traits I can mix in and combine these into test case
classes when they are required.

The latter mentioned trait would benefit from a traits implementation with
state, though.

Am So., 31. März 2019 um 21:21 Uhr schrieb Levente Uzonyi <
leves at caesar.elte.hu>:

> On Sat, 30 Mar 2019, David T. Lewis wrote:
> > Changing the subject line to focus on Levente's question.
> >
> > On Thu, Mar 28, 2019 at 06:43:11PM +0100, Levente Uzonyi wrote:
> >>
> >> What are the current use cases for traits?
> >
> > In order to experiment with Git based repositories, I have loaded the
> > Tonel package from the github repositories of Jakob Reschke.
> >
> >       Installer ensureRecentMetacello.
> >       (Smalltalk classNamed: #Metacello) new
> >          repository: 'github://j4yk/tonel:squeak';
> >          baseline: 'Tonel';
> >          load.
> >
> > This brings in the FS-AnsiStreams package, which uses traits.
> >
> > Having traits in Squeak allows me to load this package.
> I haven't tried your snippet and I don't know which version of FS depends
> on Traits, but the one on SqueakSource definitely does not.
> Btw, Traits can be flattened, so it's possible to make it loadable into
> images with no Trait support.
> So far all use cases of Traits in this thread (and its parent) were about
> interfaces. Squeak doesn't have a concept for that, and Traits are
> definitely more than just simple interfaces (as long as you don't want to
> interface state). Perhaps we need interfaces instead of traits.
> Levente
> >
> > Dave
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