RE: [mdt-ocl.dev] Arrow accessor conversion for non-collections

[Alexander Igdalov <alexander.igdalov@xxxxxxxxx>]

Hi Ed,

 

It seems to be a weird example. Why should someone use implicit convertion to a collection and use a collection operation when there is a simpler way to express it:

 

self.wife.oclIsUndefined() implies self.wife.gender = Gender::female

?

 

Thinking more about the implicit conversion to collections using an arrow, I cannot invent any good use case where it could be helpful... It seems that it could be equally well expressed using other language constructions. Do you agree?

As regards the collection type (Bag, Set or other), I think it doesn't matter much. Set is more backwards compatible but Bag fits too.

 

Cheers,

- Alex.

---

From: mdt-ocl.dev-bounces@xxxxxxxxxxx [mailto:mdt-ocl.dev-bounces@xxxxxxxxxxx] On Behalf Of Ed Willink
Sent: Wednesday, January 20, 2010 11:47 PM
To: mdt-ocl.dev@xxxxxxxxxxx
Subject: Re: [mdt-ocl.dev] Arrow accessor conversion for non-collections

Hi Alex

The purpose of the conversion is to make 0..1 properties easy to use.

Thus in 7.5.3 "Navigation over Associations with Multiplicity Zero or One" we get

    self.wife->notEmpty() implies self.wife.gender = Gender::female

so creation of Set{null} would completely invalidate the usage.

My raised issue has now been allocated Issue 14981.

Bag{} and Set{x} are not quite contradictory, just a little inconsistent. The issue suggests
changing to Bag{} and Bag{x}, so that the compile-time type is predictable. I changed
the MDT-OCL 1.3.0 synthesis of Set{x}-> to x.oclAsCollection()-> so that the null-ness
of x determines the collection content. Unfortunatel;y Collection<T> is insufficient to allow
some exiusting unit tests to work that expect Set.

    Ed


On 20/01/2010 18:35, Alexander Igdalov wrote:

Hi all,

 

The resolution of issue 10438 made `null->foo()` a synonym of `Bag{}->foo()`. As Ed has mentioned earlier this contradicts 7.5.3 which suggests wrapping the _expression_ source to a Set, i.e. `x->foo()` becomes `Set{x}->foo()` if `x` is not a collection.

 

Does anyone see why there is that exception from the general rule for null? If not I will raise an OMG issue for that.

 

Since `null->foo()` is allowed, what should it be converted to? Should it be `Set{}->foo()` or `Set{null}->foo()`? I would prefer the latter because only in this case we could construct a complete AST at compile time (see guideline at 9.6).

 

Regards,

- Alex.

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