Optional argument defaulted to Single.NaN cannot be overridden?

  • Thread starter Thread starter Joe Duchtel
  • Start date Start date
J

Joe Duchtel

Hello -

I am defaulting an optional parameter to Single.NaN so I can determine
whether it was passed in or not. The problem is when I do this in an
overriden Sub/Function it will not compile. Here is the code ...

MustInherit Class cParent
Public MustOverride Sub XYZ(Optional ByVal aA As Single =
Single.NaN)
End Class

Class cChild
Inherits cParent
Public Overrides Sub XYZ(Optional ByVal aA As Single = Single.NaN)
' ...
End Sub
End Class

This causes a 'Public Overrides Sub XYZ([aA As Single = -1.#IND])'
cannot override 'Public MustOverride Sub XYZ([aA As Single = -1.#IND)'
because they differ by the default values of optional parameters.

Is this a glitch in Visual Studio or am I doing something wrong? I
tried it in both Visual Studio 2003 (.NET 1.1) and Visual Studio 2008
(.NET 2.0, 3.0, 3.5) ...

Thanks,
Joe
 
Joe Duchtel said:
Hello -

I am defaulting an optional parameter to Single.NaN so I can determine
whether it was passed in or not. The problem is when I do this in an
overriden Sub/Function it will not compile. Here is the code ...

MustInherit Class cParent
Public MustOverride Sub XYZ(Optional ByVal aA As Single =
Single.NaN)
End Class

Class cChild
Inherits cParent
Public Overrides Sub XYZ(Optional ByVal aA As Single = Single.NaN)
' ...
End Sub
End Class

This causes a 'Public Overrides Sub XYZ([aA As Single = -1.#IND])'
cannot override 'Public MustOverride Sub XYZ([aA As Single = -1.#IND)'
because they differ by the default values of optional parameters.

Is this a glitch in Visual Studio or am I doing something wrong? I
tried it in both Visual Studio 2003 (.NET 1.1) and Visual Studio 2008
(.NET 2.0, 3.0, 3.5) ...

Thanks,
Joe
Click to expand...


I suspect that the reason is that checking dim b as Boolean = (Single.NaN =
Single.NaN) returns false.

MSDN Says:

Use IsNaN to determine whether a value is not a number. It is not possible
to determine whether a value is not a number by comparing it to another
value equal to NaN.

I don't know a work arround for your situation.
 
In my opinion you could solve this in 2 ways

1 encapsulate the method in a object and set the field ( or not ) with a
property
2 use one of the other contstants that do work but are out of range for your
purposes ( like Single.NegativeInfinity or Single.PositiveInfinity )


HTH

Michel Posseth
 
Below is a different approach using ParamArray. It gains by letting you
detect when zero parameters were passed. It loses by allowing more than one
parameter to be passed.

MustInherit Class cParent
Public MustOverride Sub XYZ(ByVal ParamArray aA() As Single)
End Class

Class cChild
Inherits cParent
Public Overrides Sub XYZ(ByVal ParamArray aA() As Single)
' aA.Length is the number of parameters passed
' if aA.Length=0, no parameters were passed
' if aA.Length=1, one parameter is in aA(0)
' if aA.Length=2, two parameters are in aA(0) and aA(1)
' etc
End Sub
End Class
 
In my opinion you could solve this in 2 ways

1 encapsulate the method in a object and set the field ( or not ) with a
property
2 use one of the other contstants that do work but are out of range for your
purposes ( like Single.NegativeInfinity or Single.PositiveInfinity )

HTH

Michel Posseth

"Joe Duchtel" <[email protected]> schreef in bericht

Hello -
Click to expand...
I am defaulting an optional parameter to Single.NaN so I can determine
whether it was passed in or not.  The problem is when I do this in an
overriden Sub/Function it will not compile.  Here is the code ...
Click to expand...
MustInherit Class cParent
   Public MustOverride Sub XYZ(Optional ByVal aA As Single =
Single.NaN)
End Class
Click to expand...
Class cChild
   Inherits cParent
   Public Overrides Sub XYZ(Optional ByVal aA As Single = Single.NaN)
       ' ...
   End Sub
End Class
Click to expand...
This causes a 'Public Overrides Sub XYZ([aA As Single = -1.#IND])'
cannot override 'Public MustOverride Sub XYZ([aA As Single = -1.#IND)'
because they differ by the default values of optional parameters.
Click to expand...
Is this a glitch in Visual Studio or am I doing something wrong?  I
tried it in both Visual Studio 2003 (.NET 1.1) and Visual Studio 2008
(.NET 2.0, 3.0, 3.5) ...
Click to expand...
Thanks,
Joe- Hide quoted text -
Click to expand...

- Show quoted text -
Click to expand...

Hello Michel -

I do not have the NegativeInfinity nor PositiveInfinity in Visual
Studio 2003 (.NET 1.1) and that is currently the main development
platform. I will think about your first suggestion ... there might be
a way I could do it like that.

Thanks,
Joe
 
Below is a different approach using ParamArray.  It gains by letting you
detect when zero parameters were passed.  It loses by allowing more than one
parameter to be passed.

MustInherit Class cParent
  Public MustOverride Sub XYZ(ByVal ParamArray aA() As Single)
End Class

Class cChild
  Inherits cParent
  Public Overrides Sub XYZ(ByVal ParamArray aA() As Single)
    ' aA.Length is the number of parameters passed
    ' if aA.Length=0, no parameters were passed
    ' if aA.Length=1, one parameter is in aA(0)
    ' if aA.Length=2, two parameters are in aA(0) and aA(1)
    ' etc
  End Sub
End Class
Click to expand...

Hello -

The ParamArray is a great idea but the example I posted is only a
simplified version of the interface. There is more than one optional
argument and some mandatory arguments as well. The problem is that
the optional arguments are of different types (e.g. String) so I could
not replace them by a single ParamArray and mixing the Optional with
the ParamArray will not work.

Thanks,
Joe
 
Joe said:
Hello -

I am defaulting an optional parameter to Single.NaN so I can determine
whether it was passed in or not. The problem is when I do this in an
overriden Sub/Function it will not compile. Here is the code ...

MustInherit Class cParent
Public MustOverride Sub XYZ(Optional ByVal aA As Single =
Single.NaN)
End Class

Class cChild
Inherits cParent
Public Overrides Sub XYZ(Optional ByVal aA As Single = Single.NaN)
' ...
End Sub
End Class

This causes a 'Public Overrides Sub XYZ([aA As Single = -1.#IND])'
cannot override 'Public MustOverride Sub XYZ([aA As Single = -1.#IND)'
because they differ by the default values of optional parameters.

Is this a glitch in Visual Studio or am I doing something wrong? I
tried it in both Visual Studio 2003 (.NET 1.1) and Visual Studio 2008
(.NET 2.0, 3.0, 3.5) ...
Click to expand...


I'd use Nullable(Of Single) instead. Though, not available in .Net 1.1.


Armin
 
Armin Zingler said:
Joe said:
Hello -

I am defaulting an optional parameter to Single.NaN so I can determine
whether it was passed in or not. The problem is when I do this in an
overriden Sub/Function it will not compile. Here is the code ...

MustInherit Class cParent
Public MustOverride Sub XYZ(Optional ByVal aA As Single =
Single.NaN)
End Class

Class cChild
Inherits cParent
Public Overrides Sub XYZ(Optional ByVal aA As Single = Single.NaN)
' ...
End Sub
End Class

This causes a 'Public Overrides Sub XYZ([aA As Single = -1.#IND])'
cannot override 'Public MustOverride Sub XYZ([aA As Single = -1.#IND)'
because they differ by the default values of optional parameters.

Is this a glitch in Visual Studio or am I doing something wrong? I
tried it in both Visual Studio 2003 (.NET 1.1) and Visual Studio 2008
(.NET 2.0, 3.0, 3.5) ...
Click to expand...


I'd use Nullable(Of Single) instead. Though, not available in .Net 1.1.


Armin
Click to expand...

That wouldn`t work as nullable datatypes are not allowed as optional
parameters

Michel
 
Michel said:
This causes a 'Public Overrides Sub XYZ([aA As Single = -1.#IND])'
cannot override 'Public MustOverride Sub XYZ([aA As Single =
-1.#IND)' because they differ by the default values of optional
parameters.

Is this a glitch in Visual Studio or am I doing something wrong? I
tried it in both Visual Studio 2003 (.NET 1.1) and Visual Studio
2008 (.NET 2.0, 3.0, 3.5) ...
Click to expand...


I'd use Nullable(Of Single) instead. Though, not available in .Net
1.1.


Armin
Click to expand...

That wouldn`t work as nullable datatypes are not allowed as optional
parameters
Click to expand...

Using Nullable, the parameter does not have to be optional anymore.


Armin
 
Armin Zingler said:
Michel said:
This causes a 'Public Overrides Sub XYZ([aA As Single = -1.#IND])'
cannot override 'Public MustOverride Sub XYZ([aA As Single =
-1.#IND)' because they differ by the default values of optional
parameters. Is this a glitch in Visual Studio or am I doing something
wrong? I
tried it in both Visual Studio 2003 (.NET 1.1) and Visual Studio
2008 (.NET 2.0, 3.0, 3.5) ...


I'd use Nullable(Of Single) instead. Though, not available in .Net
1.1. Armin
Click to expand...

That wouldn`t work as nullable datatypes are not allowed as optional
parameters
Click to expand...

Using Nullable, the parameter does not have to be optional anymore.


Armin
Click to expand...

I thought about that too ( you know that i actually had the same idea ) but
in that case he must always suply a parameter value even if it is Nothing
and i just guess that this is exactly what he did not want in the first
place

or am i missing something here ?

regards

Michel
 
Michel said:
Armin Zingler said:
Michel said:
This causes a 'Public Overrides Sub XYZ([aA As Single = -1.#IND])'
cannot override 'Public MustOverride Sub XYZ([aA As Single =
-1.#IND)' because they differ by the default values of optional
parameters. Is this a glitch in Visual Studio or am I doing
something wrong? I
tried it in both Visual Studio 2003 (.NET 1.1) and Visual Studio
2008 (.NET 2.0, 3.0, 3.5) ...


I'd use Nullable(Of Single) instead. Though, not available in .Net
1.1. Armin

That wouldn`t work as nullable datatypes are not allowed as optional
parameters
Click to expand...

Using Nullable, the parameter does not have to be optional anymore.


Armin
Click to expand...

I thought about that too ( you know that i actually had the same idea
) but in that case he must always suply a parameter value even if it
is Nothing and i just guess that this is exactly what he did not want
in the first place

or am i missing something here ?
Click to expand...

I should have added that I'd overload the function then.

Public MustOverride Sub XYZ()
Public MustOverride Sub XYZ(ByVal aA As Nullable(of Single))

'inheriting class:

Public Overrides Sub XYZ()
XYZ(Nothing) 'Or is there a better way to pass
'a nullable type with HasValue = False?
End Sub

Public Overrides Sub XYZ(ByVal aA As Nullable(of Single))
if aA.HasValue then
else
end if
End Sub


Armin
 
Armin Zingler said:
Michel said:
Armin Zingler said:
Michel Posseth [MCP] wrote:
This causes a 'Public Overrides Sub XYZ([aA As Single = -1.#IND])'
cannot override 'Public MustOverride Sub XYZ([aA As Single =
-1.#IND)' because they differ by the default values of optional
parameters. Is this a glitch in Visual Studio or am I doing
something wrong? I
tried it in both Visual Studio 2003 (.NET 1.1) and Visual Studio
2008 (.NET 2.0, 3.0, 3.5) ...


I'd use Nullable(Of Single) instead. Though, not available in .Net
1.1. Armin

That wouldn`t work as nullable datatypes are not allowed as optional
parameters

Using Nullable, the parameter does not have to be optional anymore.


Armin
Click to expand...

I thought about that too ( you know that i actually had the same idea
) but in that case he must always suply a parameter value even if it
is Nothing and i just guess that this is exactly what he did not want
in the first place

or am i missing something here ?
Click to expand...

I should have added that I'd overload the function then.

Public MustOverride Sub XYZ()
Public MustOverride Sub XYZ(ByVal aA As Nullable(of Single))

'inheriting class:

Public Overrides Sub XYZ()
XYZ(Nothing) 'Or is there a better way to pass 'a nullable type
with HasValue = False?
End Sub

Public Overrides Sub XYZ(ByVal aA As Nullable(of Single))
if aA.HasValue then
else
end if
End Sub


Armin
Click to expand...


You convinced me with this construction :-) ,
i would recomend the TS to keep this construction in mind when upgrading

regards

Michel
 
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