I don't remember me wanting a collect: to return a set any time of my life, so
I would agree.
Clara Allende schrieb:
I would spect it to return aBag, for example.
On 27 October 2011 12:13, Andrea Brühlmann <[email protected]> wrote:
Hi Clara,
You don't need to worry about the receivers class, but about the result you
wish to have... There are 2 possibilities what the result will be: either
the same kind as the original collection or something else! If you mind
about the result, you need to tell the system what the result should look
like :-)
But I just want to use it!
In your case, it is important that the result is no Set, so this is why you
need to tell the system to collect the grades as an OrderedCollection or
whatever. It doesn't matter if the students are a Set or not then!
Indeed. IN THIS CASE it's important that the result is not a Set. But why?
Because the receiver is a Set!!! I do not send a asBag message to every
collect: result I get, so why should I do that here? What you're saying is
that I need to be aware that the receiver is a Set, which sucks. Otherwise,
I should send asBag every time I use collect:, just in case the receiver is
a Set... That doesn't sound good.
self students collect: #grade as: OrderedCollection
Do you have another solution in mind? Maybe you expect Set>collect: to
return anOrderedCollection by Default? This would make sense for your
students grades and for many more cases, but then, the implementation would
break the rule "Collections always return results on an new instance of its
own #species".
And why couldn't we break the rule in this case? Again, this works for the
others collections and the other messages, and I'm ok with it. But not with
collect: :S
Andrea
Clara Allende schrieb:
Ok, but this means I have to worry of the receiver's class before I send
collect:, so as I don't fuck it all up.... and I don't want to think about
that!!! See, if I want the collection of grades of the students, I would
like to do this:
grades
^self students collect: [.aStudent | aStudent grades]
regardless of whatever is the class of students... This does the trick
for
all the collections, except for Set. And I don´t know if students is an
instance of Set, and I really don't want to think if it is or not. If I
don't want repeated students and I create my collection as an instance of
Set, an i.e.; I want to calculate the average, then I'm screwed because
the
collection I get from the collect: wasn't the want that I wanted.
So, I have to know previously that my collection is an instance of Set, or
if it isn't, so as to know if I have to convert it first....
And if I use collect: as:, as you suggest, this means the collections are
no
longer polymorphic for me :(
Sorry, maybe I'm really stupid, but I don't know how that message solves
best the problem than redefining collect: for Set. For the particular case
I
don't want the repeated objects (which AFAIK is not so common) I could
send
asSet.
On 27 October 2011 11:05, Henrik Sperre Johansen <
[email protected]> wrote:
On 27.10.2011 15:40, Clara Allende wrote:
I know, but our students don't :) So they ran into problems because the
message send didn't answer what they were specting.... because it makes
sense that if I want to transform the objects in my collection, I might
get
repeated objects... Maybe I'm not thinking in terms of consistency, I'm
just
putting myself on student's shoes :P
The consistency rule to remember for #collect:/#select:/#reject: is
that
they will return a collection of the receiver's species.
#collect:as: was added as a general answer to the situation your students
ran into :)
set := Set withAll: #(1 2 3 4 5 6 7 8).
result := set collect: #even as: Bag.
Cheers,
Henry
