On Wed, 2011-08-31 at 16:34 +0200, Benoît Minisini wrote:
> This is one the design rule of Gambas : a method has to always return
> the same
> datatype, otherwise it must return a Variant.
Benoît,
I think you may have missed the point of my, albeit "contrived", sample.
On the other hand I may not have made it explicit enough to let you
answer my fears. I'll try again:
Emil gave an example where the result "a" of a loop construct was one of
two closely related object references:
"For i = 1 To 2
If i = 1 Then
a = New Class1
Else If i = 2 Then
a = New Class2
End If
Print a.F() + i 'Will print the address in memory for "2" + i the second time
Next"
There is a hidden artefact in this code in that a (an object reference)
is of a particular inheritance sequence. However, because both Class1
and Class2 both have explicit and in the case of Class2 an overridding
implementation of an attribute called F the interpreter has optimised
that "any a.F will be an integer", which is not true in the case where a
happens to be a Class2.
In resolving this issue you have spent a great deal of time and effort
on introducing a "rule" that says, to me at least, "once F is declared
in Class1, then any specialised class of Class1 "must" declare F of the
same type,scope and signature as was declared in Class1. Please don't
react yet.
Just consider the replacement of the original code with this:
"For i = 1 To infinty
Select case Int(Random(i:infinty))
Case 1
a = new Class1
Case 2
a = new Class2
Case 3
a = Object.New("gorilla")
....
Case 23165
a= Object.New("blue_whale")
Case 23166
a=Object.New("bowl_of_petunias")
....
Case 10^2134532 and falling
a=Object.New("trillian")
....
Case infinity-1
a=Object.New("marvin")
Case else
' I'll leave THAT for the readers homework
End Select
' Now magically and against all levels of improbability all of these classes
just "happen" to have a method
' called "F". Strange, but not altogether improbable.
Print a.F() + i 'Will succeed, somehow in some format, or not
Next"
the original code, at an improbability level of 2^3498423432 just
happened to include a situation where on the first invocation
Int(Random(i:infinty)) was 1 and even more strangely on the second
invocation Int(Random(i:infinty)) just happened to be 2. Many pundits
and philosophers have argued over exceedingly long lunches as to how
this came about, but at the end of the day disagreed. Which only gave
them the opportunity to have lunch again sometime, preferably before or
at the end of the Universe.
OK, enough of my reminiscing of Doug Anderson.
For i =1 to 2
a="something"
PRINT a.F()
Next
Just because a happens to have a method called F, there should be no
RULE that a.F(), which happened to be an integer the first time is an
integer the second. It could be a small furry beast from Alpha
Centauri.
Emil's example, in my opinion, has sent you off on a search for an
explicit answer to the highly improbable sequence
Int(Random(i:infinty)={1,2} where Class1 and Class2 are related through
inheritance. His "a" is an object reference which just happens to have
a method "F" which returns an integer. Your optimization rule seems to
be "any a.F() is an integer". I hope that through the above ramble, I
have illustrated that such a supposition cannot be considered to be true
in all instances.
Putting that another way, any expression that includes a reference to an
object cannot EXPECT that an instance within a (subsequent) iteration IS
going to return a SPECIFIC TYPE based on prior experience.
Benoit, I am Australian and therefore have a poor level of expressing
myself objectively and unemotively, in the English language.
Please Consider.
regards
Bruce
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