On Apr 16, 2007, at 1:52 PM, Dennis Birch wrote:
> On 4/16/07, Norman Palardy <[EMAIL PROTECTED]> wrote:
>>
>> On 16-Apr-07, at 11:38 AM, Dennis Birch wrote:
>>
>>> On 4/16/07, Charles Yeomans <[EMAIL PROTECTED]> wrote:
>>>>
>>>> On Apr 16, 2007, at 12:26 PM, Dennis Birch wrote:
>>>>
>>>>> Is it possible to not return an instance of a class from its
>>>>> constructor?
>>>
>>>> Not exactly. If you want to return nil if the constructor fails,
>>>> then you can define a shared method NewSomeClass(rs as
>>>> RecordSet) as
>>>> SomeClass and call it.
>>>
>>> Thanks Charles. I'm a little confused about this approach. Can you
>>> elaborate?
>>
>> You don't use the constructor directly.
>> You use a shared method that returns an instance of your class.
>> It becomes a factory (something that makes instances of the class)
>
> Thanks Norman. In other words, you're talking about creating a
> fallback that builds an instance of my class with default values?
Not quite. You should do something like the following.
Sub Constructor(rs as RecordSet)
if rs is nil then
raise new RuntimeException //replace with a more descriptive
subclass
end if
if rs.Field("Foo") is nil then
raise new RuntimeException //replace with a more descriptive
subclass
end if
//now that you have verified parameter, proceed with initialization
End Sub
Some people prefer to test the return value of a function for nil
instead of catching exceptions. NewSomeClass is a shared method.
Shared Function NewSomeClass(rs as RecordSet) as SomeClass
return new SomeClass
exception theError as RuntimeException
return nil
End Function
In other code, you might write
dim foo as SomeClass = SomeClass.NewSomeClass
if foo is nil then
...
Charles Yeomans
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