On Tue, Jun 6, 2017 at 1:26 AM, Vitor Medina Cruz <vitormc...@gmail.com>
wrote:
> 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.
>
I guess I don't properly understand your need and those topics. That was
my quick pass. Now if I take the time to actually read Fowler's long
article
"the inversion is about how they lookup a plugin implementation ... to
ensure that any user of a plugin follows some convention that allows a
separate assembler module to inject the implementation into the lister."
"The basic idea of the Dependency Injection is to have a separate object,
an assembler, that populates a field in the lister class with an
appropriate implementation for the finder interface. There are three main
styles of dependency injection. The names I'm using for them are
Constructor Injection, Setter Injection, and Interface Injection."
Now there was too much syntactical noise in those Java examples for me to
think clearly, so I converted them all to Smalltalk.
##CONSTRUCTOR INJECTION
Object subclass: MovieLister
instanceVariables: 'finder'
MovieLister class >> newWith: aFinder
^ self basicNew initializeWith: aFinder
MovieLister >> initializeWith: aFinder
finder := aFinder
ColonMovieFinder class >> newWith: aFilename
^ self basicNew initializeWith: aFilename
ColonMovieFinder >> initializeWith: aFilename
filename := aFilename.
ConstructorInjectionContainer >> new
container := DefaultContainer new. "the article doesn't specify where
this comes from"
finderParams := ConstantParameter newWith: 'movies1.txt'.
container registerComponentInterface: MovieFinderInterface
implementation: ColonMovieFinder
params: finderParams.
container registerComponentImplementation: MovieLister
^container
to be used like this...
ConstructorInjectionTest >> testWithContainer
container := ConstructorInjectionContainer new.
lister := container getComponentInstance( MovieLister ).
movies = lister moviesDirectedBy: 'Sergio Leone'.
self assert: (movies includes: 'Once Upon a Time in the West')
The article poorly defines registerComponentXXX: or getComponentInstance:
methods, so I don't dwell on them. I presume its little relevant to the
main theme.
##SETTER INJECTION
MovieLister >> setFinder: aFinder
finder := aFinder.
ColonMovieFinder >> setFilename: aFilename
filename := aFilename.
SetterInjectionTest >> testWithConfigurationFile
ctx := SomeXmlApplicationConfiguration on: 'config.xml'.
lister := ctx getConfigOf: 'MovieLister'.
movies = lister moviesDirectedBy: 'Sergio Leone'.
self assert: (movies includes: 'Once Upon a Time in the West')
##INTERFACE INJECTION
MovieLister >> injectFinder: aFinder
finder := aFinder
ColonMovieFinder >> injectFilename: aFilename
filename := aFilename
InterfaceInjectionTest >> configureContainer
container := InterfaceInjectionContainer new.
self registerComponents.
self registerInjectors.
container start.
InterfaceInjectionTest >> registerComponents
container registerComponent: 'MovieLister' with: MovieLister.
container registerComponent: 'MovieFinder' with: ColonMovieFinder.
InterfaceInjectionTest >> registerInjectors
container registerInjector: Injector with: (container lookup:
'MovieFinder').
container registerInjector: InjectorFinderFilename with:
FinderFilenameInjector new.
ColonMovieFinder >> inject: anObject
anObject injectFinder: self.
FinderFilenameInjector >> inject: anObject
anObject injectFilename: 'movies1.txt'.
InterfaceInjectionTester >> testInterface
self configureContainer.
lister := container lookup: 'MovieLister'.
movies = lister moviesDirectedBy: 'Sergio Leone'.
self assert: (movies includes: 'Once Upon a Time in the West')
The article doesn't define InterfaceInjectionContainer, but I guess it
could look like this...
InterfaceInjectionContainer >> registerComponent: componentName with:
aComponent
container ifNil: [ container := Dictionary new].
container at: componentName put: aComponent
InterfaceInjectionContainer >> lookup: componentName
^ container at: componentName
##SERVICE LOCATOR
"The basic idea behind a service locator is to have an object that knows
how to get hold of all of the services that an application might need. So a
service locator for this application would have a method that returns a
movie finder when one is needed. Of course this just shifts the burden a
tad, we still have to get the locator into the lister"
MovieLister >> initialize
finder := ServiceLocator movieFinder.
Object subclass: ServiceLocator
instanceVariable: 'movieFinder'
classVariable: 'SoleInstance'
ServiceLocator class >> load: aServiceLocator
SoleInstance := aServiceLocator
ServiceLocator class >> soleInstance
^ SoleInstance
ServiceLocator class >> movieFinder
^ self soleInstance movieFinder
ServiceLocator >> movieFinder
^movieFinder
ServiceLocatorTest >> configure
ServiceLocator load: (ServiceLocator newWith: (ColonMovieFinder
newWith: 'movies1.txt'))
ServiceLocator class >> newWith: aMovieFinder
^ self basicNew initializeWithFinder: aMovieFinder
ServiceLocator >> initializeWithFinder: aMovieFinder
movieFinder := aMovieFinder
ServiceLocatorTest >> testSimple
self configure.
lister := MovieLister new.
movies = lister moviesDirectedBy: 'Sergio Leone'.
self assert: (movies includes: 'Once Upon a Time in the West')
So it seems that a service locator is just a Singleton pattern having a
class variable for each service of interest ??
So in good faith** I ask... "Is it any more complicated than that?"
**Since its taken me a couple of hours to convert the Java to this point so
I stopped reading to seek your feedback.
Is that enough insight to adapt to your needs, or is there something else
further down the article that invalidates my analysis?
>
> 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'."
>
>
So per Fowler, the above is equivalent to "Setter Injection with Spring"
>
> 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
>
No, like this...
finder := ServiceLocation movieFinder.
Now if you want to store a class rather than an instance as I did higher
up, you just do this...
Object subclass: ServiceLocator
instanceVariable: 'movieFinderClass'
classVariable: 'SoleInstance'
ServiceLocator class >> movieFinder
^ self soleInstance movieFinderClass new
>
>
> 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
>
Assembler class>>configure
ServiceLocator load:
(ServiceLocator new
movieFinder: (ColonMovieFinder newWith: 'movies1.txt')
otherService: MyCustomService new)
>
> My assembler and service locator could be even more elaborated, and
> provide a different MovieFinder in test scope, for different classes or
> wharever.
>
Really, the test should not be updating the class variable global like
this...
ServiceLocatorTest >> configure
ServiceLocator load: (ServiceLocator newWith: (ColonMovieFinder
newWith: 'movies1.txt'))
you probably want something like (its rough but shows the point...)
Object subclass: #MovieLister
instanceVariables: 'serviceLocator'
MovieLister >> initialize
serviceLocator ifNil: [ serviceLocator := ServiceLocator soleInstance ].
finder := serviceLocator movieFinder.
MovieLister class >> newWithServiceLocator: aServiceLocator
^ (self basicNew initializeWithServiceLocator: aServiceLocator)
initialize.
MovieLister >> initializeWithServiceLocator: aServiceLocator
serviceLocator := aServiceLocator
ServiceLocatorTest >> testSimple2
lister := MovieLister newWithServiceLocator: (ServiceLocator newWith:
(ColonMovieFinder newWith: 'movies1.txt')).
movies = lister moviesDirectedBy: 'Sergio Leone'.
self assert: (movies includes: 'Once Upon a Time in the West')
cheers -ben
>
> 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.
>
>
>
> 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#FormsOfDepe
>> ndencyInjection:
>> >
>> > "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-depen
>> dency-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
>> >
>> >
>> >
>>
>>
>
