Joseph Wakeling wrote:
>> - opCall() of AvgWeighted was abstract.
>> - keep in mind that in D classes are CamelCase;
>> - variable names are written like weightSum (but once in a while a
underscore
> doesn't kill).
>
> I think it's obvious from my syntax that my background is with C; I'm not
> experienced with Java, C# etc. This may explain some of the problems
I'm having.
>
> Regarding opCall I was following the syntax described here:
> http://www.digitalmars.com/d/2.0/operatoroverloading.html#FunctionCall
>
> ... but clearly without understanding it properly.
I have experience with C++ and still don't understand why opCall exists.
:) I think I heard that opCall was needed to create struct objects
before structs had constructors in D.
Now structs do have constructors, which sometimes conflict with opCall. :)
> What I was aiming for was a bit smartarse -- to have a class which
could in some
> cases be treated as a function.
I consider myself a function-happy programmer. To me, not everything is
a class. :)
> Each of these classes (later ones will be more
> sophisticated) is meant to be a data analysis tool which takes a
dataset of
> user-object ratings and user and object reputation values and helps
aggregate the
> ratings and in the process update the reputation values.
>
> The aim was that if you just wanted a once-off analysis you could use
the class in
> a throwaway fashion -- hence the use of,
>
> avg_weighted(......);
It could be a function that instantiates on object, that would be thrown
away.
> It's maybe not the best way to approach what I want to do, but since
D is a new
> language for me, I thought I would be playful with it and try and
bend it around
> in some interesting ways.
No harm in that. :)
>> - Be careful because ref arguments are tricky.
>
> The choice is deliberate here, because the arrays passed to the
constructor (or
> opCall) are meant to be modified.
D has "reference types". When you pass a class object to a function
"by-value", it is actually passed-by-reference. I think this is the same
in Java.
You can imagine the function parameter being a pointer behind the scenes.
ClassType variable = new ClassType;
ClassType variable2 = variable;
You have a single "object" created with new, and two "variables" that
refer to that object.
>> - There is a line like foreach (r; reputationUser) r = 1; that can
be a bug.
>
> I guess that I should put a 'double' in front of the r, no? In any
case, I guess
> there is a better way of setting all elements of an array equal to 1.0.
You would put 'ref' in front of the foreach variables. Otherwise they
are copies in the foreach loop.
>> - foreach (objectID, rating; reputationObject) rating /=
weightSum[objectID];
> can be another bug.
>
> ... so should be uint objectID, double rating ... ?
Same: Should probably be 'ref rating' if you want to modify
reputationObject.
> I think it's obvious that I want each the value of each element of
> reputationObject to be divided by the value of the corresponding
element of
> weightSum -- is there a more intelligent way of doing this?
>> - I suggest to add contracts and unittests.
>
> As you might have guessed, I'm not a developer -- can you provide
more info?
They are of the greater features of D. :) You can define function pre-
and post-conditions and struct and class invariants. You can have
unittest blocks... Great stuff! :)
http://digitalmars.com/d/2.0/unittest.html
http://digitalmars.com/d/2.0/dbc.html
http://digitalmars.com/d/2.0/class.html#Invariant
Ali
