Re: Call by Result
On 17/06/2011 10:40, lewbloch wrote:
On Jun 16, 7:30 am, Cholo Lennon<chololen...@hotmail.com> wrote:
On 10/06/2011 03:03, Gene Wirchenko wrote:
Dear Java'ers:
I wish to call by result with a method. Is it possible? If not,
can it be easily simulated in an unnasty way?
I am writing a simple preprocessor. I have a few spots where a
string needs to be parsed. I want to call something like this:
String ReturnString="";
boolean DidItWork=GetString(ReturnString);
if (!DidItWork)
// too bad
It is not acceptable to have a special String value mean failure. I
want the method to be able to return any potential string.
Sincerely,
Gene Wirchenko
IMHO using exceptions is not always the best answer to this problem (as
other suggested).
How about using a simple generic class? (of course, it could be
corrected or improved. A similar idea could be found in other languages
(such as C++ (boost)):
class Optional<T> {
private T value;
private boolean valid;
public Optional(T value) {
setValue(value);
It's dangerous to call an overridable method from a constructor.
Agree, you're right. It was for simplicity.
}
public Optional() {
this.valid = false;
Redundant assignment, but arguably it adds clarity. I don't think it
does, but one could argue that it does.
Agree, you're right, it was written for clarity.
}
public boolean isValid() {
return this.valid;
}
public T getValue() {
return this.value;
}
public void setValue(T value) {
this.value = value;
// TODO Shall I set to true when value is null?
this.valid = true;
}
public void invalidate() {
this.value = null;
this.valid = false;
}
}
The original post establishes 'null' as an out-of-band value. Your
code hints at that possibility in a comment, but doesn't enforce the
requirement. If 'null' is out of band, then the boolean variable is
redundant and duplicative. If 'null' is in band, then the boolean
makes more sense, as it would have to to justify the complexity.
Well, the class presents a general solution. Maybe Null could be a valid
value. But you're right, for sake of simplicity I think it's better to
get rid of the boolean variable. If this is the case, we have a
'Nullable' class (see Dot Net version at
http://msdn.microsoft.com/en-us/library/b3h38hb0.aspx)
--
Lew
Regards
--
Cholo Lennon
Bs.As.
ARG