Thanks for the answer Ben and Stephane.
I already read A Mentoring Course on Smalltalk, Valloud, there is nothing
there I could use in this case :( . I will look after for The Design
Patterns Smalltalk Companion. Most of the sources provided I already know
of or went in the same lines lines of what I have already found.
About TDD, I am experienced with the discipline and have tested it on Pharo
living system already, but I could not understand how this is related with
object wiring, DI and service locator.
>From ben:
"I'm not really familiar with IoC or DI patterns, so just taking your
> example at face value, in Pharo I'd do...
>
> MovieLister>>moviesDirectedBy: director
> allMovies := finder allMovies.
> ^ allMovies select: [ :movie | movie getDirector = director ].
> "although typically #getDirector would be renamed #director"
>
> MovieLister>>finder: movieFinder
> finder := movieFinder.
>
> to be used like this...
> lister := MovieLister new finder: (ColonDelimitedMovieFinder on:
> 'movies1.txt').
> movies := lister moviesDirectedBy: 'Tarantino'."
and Stephane:
Why don't you simply pass the class and use that class in your MovieLister?
>
> MovieLister new
> finderClass: MySuperCoolFinderClass
>
> ...
> MovieLister finder
> finderClass new .....
>
> What is wrong with that.
That was what I meant when I said: "I know that in Smalltalk I can make
MovieLister to receive, upon construction, a class representing MovieFinder
and call it construction message.". The code I had in mind is a bit of mix
from the one provided by you both:
MovieLister>>moviesDirectedBy: director
allMovies := finder allMovies.
^ allMovies select: [ :movie | movie getDirector = director ].
"although typically #getDirector would be renamed #director"
MovieLister>>finder: aMovieFinderBuilder
finder := aMovieFinderClass new.
to be used like this...
lister := MovieLister new finder: (ColonDelimitedMovieFinder builderOn:
'movies1.txt').
movies := lister moviesDirectedBy: 'Tarantino'."
But that means I will have to wire dependencies by hand whenever I create a
MovieLister and seek through code when and if those dependencies change.
When there are lot's of dependencies it's is a considerable and tedious
work. Let's see an image from Fowlers article:
[image: Inline image 1]
In this case, the service locator provides me with an instance and I
configure the instance in the assembler, the scheme is alike for an IoC,
and that would mean my implementation could be like this:
MovieLister>>moviesDirectedBy: director
allMovies := finder allMovies.
^ allMovies select: [ :movie | movie getDirector = director ].
"although typically #getDirector would be renamed #director"
MovieLister>>initialize
finder := ServiceLocator locate: FinderClass <--- This would bring
the instance of finder class configured by the assembler
to be used like this...
lister := MovieLister new.
movies := lister moviesDirectedBy: 'Tarantino'."
and the assembler:
Assember class>>configure:
aMap put: (ColonDelimitedMovieFinder builderOn: 'movies1.txt') at:
FinderClass
My assembler and service locator could be even more elaborated, and provide
a different MovieFinder in test scope, for different classes or wharever.
It is a little convenience for Smalltalk, I will give that, but I was
wandering if there was something alike in Pharo, by your answers I assuming
there is nothing like that.
If you do not want to have a reference at runtime to a Finder then you
> need to use announcement and registration.
I didn't understand that, could you elaborate?
On Mon, Jun 5, 2017 at 6:41 AM, Stephane Ducasse <stepharo.s...@gmail.com>
wrote:
> Why don't you simply pass the class and use that class in your MovieLister?
>
> MovieLister new
> finderClass: MySuperCoolFinderClass
>
> ...
> MovieLister finder
> finderClass new .....
>
> What is wrong with that.
>
> If you do not want to have a reference at runtime to a Finder then you
> need to use announcement and registration.
>
> Stef
>
>
>
> On Sun, Jun 4, 2017 at 11:17 PM, Vitor Medina Cruz <vitormc...@gmail.com>
> wrote:
> > Hello,
> >
> > I would like to know how people in Pharo ecosystem do to deal with object
> > wiring, as described by Marting Fowler in
> > https://martinfowler.com/articles/injection.html#
> FormsOfDependencyInjection:
> >
> > "A common issue to deal with is how to wire together different elements:
> how
> > do you fit together this web controller architecture with that database
> > interface backing when they were built by different teams with little
> > knowledge of each other."
> >
> > He gives an example, I will leave it in java as it is simple enough to
> > understand:
> >
> > "class MovieLister...
> >
> > public Movie[] moviesDirectedBy(String arg) {
> > List allMovies = finder.findAll();
> > for (Iterator it = allMovies.iterator(); it.hasNext();) {
> > Movie movie = (Movie) it.next();
> > if (!movie.getDirector().equals(arg)) it.remove();
> > }
> > return (Movie[]) allMovies.toArray(new Movie[allMovies.size()]);
> >
> > }"
> >
> > The question is how to provide the finder object in a decoupled matter, a
> > naive approach would be:
> >
> > " private MovieFinder finder;
> >
> > public MovieLister() {
> > finder = new ColonDelimitedMovieFinder("movies1.txt");
> >
> > }"
> >
> > Which couples the MovieLister to the specific ColonDelimitedMovieFinder
> > class.
> >
> > Fowler explains how to decouple using an IoC framework or a Service
> Locator.
> > In Java and .Net IoC is used most of the time. I Googled how this
> problem is
> > approached in Smalltalk/Pharo, and I generally I found answers "that is
> easy
> > to do in Smalltalk, so there is no need of a framework", what I miss is a
> > description on *how* to do that:
> >
> > https://stackoverflow.com/questions/243905/smalltalk-and-ioc
> > https://stackoverflow.com/questions/2684326/is-there-a-
> dependency-injection-framework-for-smalltalk
> > https://stackoverflow.com/questions/243905/smalltalk-
> and-ioc/347477#347477
> >
> > I know that in Smalltalk I can make MovieLister to receive, upon
> > construction, a class representing MovieFinder and call it construction
> > message. As long an object that responds to this message is provided, I
> can
> > create as many derivations I want and the MovieLister will be decoupled
> from
> > the MovieFinder. That way, however, I still have to wire things by hand,
> and
> > I am not sure if this is what I am supposed to do in order to solve the
> > decouple problem.
> >
> > Can you explain me how this is done in Pharo? It's is usually wiring by
> > hand? Is there a simple construction that deals with the wiring problem
> that
> > I cannot foresee?
> >
> > Thanks in advance,
> > Vitor
> >
> >
> >
>
>
