Numeric data validation problem in class module property get/let routines

[Enigman O'Maly]

I'm still somewhat new to object style programming (as will become
evident), using VBA in Excel 2000 to automate some previously manual
functions.

I've defined a class module so that I can create objects that reflect
data gathered in web inquiries. The module has a bunch of Get/Let
routines such as this pair:

Private m_dYield As Double

Public Property Let SetYield(ByRef NewYield As Double)
m_dYield = NewYield
End Property

Public Property Get Yield() As Double
Yield = m_dYield
End Property
The problem is that zero is a valid assignment for most of these
properties, and yet I need to distinguish between a property that's been
"set" to zero versus one that has never been initialized, yet has a
default value of zero by virtue of the dimension statement. IsNull and
IsEmpty functions apparently only work with variant data types, besides
which, I dimly recall assorted VB instructors who were emphatically
against their use.

There has to be a simple solution to what must be a very common problem,
but it's got me stumped. Any suggestions are sincerely appreciated...

[Steve Gerrard]

"Enigman O'Maly" <No***@Home.com> wrote in message
news:jb********************************@4ax.com...

I'm still somewhat new to object style programming (as will become
evident), using VBA in Excel 2000 to automate some previously manual
functions.

I've defined a class module so that I can create objects that reflect
data gathered in web inquiries. The module has a bunch of Get/Let
routines such as this pair:

Private m_dYield As Double

Public Property Let SetYield(ByRef NewYield As Double)
m_dYield = NewYield
End Property

Public Property Get Yield() As Double
Yield = m_dYield
End Property
The problem is that zero is a valid assignment for most of these
properties, and yet I need to distinguish between a property that's been
"set" to zero versus one that has never been initialized, yet has a
default value of zero by virtue of the dimension statement. IsNull and
IsEmpty functions apparently only work with variant data types, besides
which, I dimly recall assorted VB instructors who were emphatically
against their use.

There has to be a simple solution to what must be a very common problem,
but it's got me stumped. Any suggestions are sincerely appreciated...

First, you Let and Get should probably match (i.e. both be Yield).
For many such properties I would agree that explicit data types are better and
faster than variants. But I hardly ever say never.
There are various ways to handle your issue. If the value of yield should be=0, you can initialize m_dYield to -1 in the class Initialize event, and tell

that way. Otherwise, you might use a second Boolean variable, m_bYieldSet, which
will initially be false, and which you make true inside of the property let
procedure for yield:
Public Property Let Yield(ByRef NewYield As Double)
m_dYield = NewYield
m_bYieldSet = True
End Property

[Enigman O'Maly]

On Fri, 10 Oct 2003 19:33:00 -0700, "Steve Gerrard"
<no*************@comcast.net> wrote:

"Enigman O'Maly" <No***@Home.com> wrote in message
news:jb********************************@4ax.com.. .

I'm still somewhat new to object style programming (as will become
evident), using VBA in Excel 2000 to automate some previously manual
functions.

I've defined a class module so that I can create objects that reflect
data gathered in web inquiries. The module has a bunch of Get/Let
routines such as this pair:

Private m_dYield As Double

Public Property Let SetYield(ByRef NewYield As Double)
m_dYield = NewYield
End Property

Public Property Get Yield() As Double
Yield = m_dYield
End Property
The problem is that zero is a valid assignment for most of these
properties, and yet I need to distinguish between a property that's been
"set" to zero versus one that has never been initialized, yet has a
default value of zero by virtue of the dimension statement. IsNull and
IsEmpty functions apparently only work with variant data types, besides
which, I dimly recall assorted VB instructors who were emphatically
against their use.

There has to be a simple solution to what must be a very common problem,
but it's got me stumped. Any suggestions are sincerely appreciated...

First, you Let and Get should probably match (i.e. both be Yield).
For many such properties I would agree that explicit data types are better and
faster than variants. But I hardly ever say never.
There are various ways to handle your issue. If the value of yield should be

=0, you can initialize m_dYield to -1 in the class Initialize event, and tell

that way. Otherwise, you might use a second Boolean variable, m_bYieldSet, which
will initially be false, and which you make true inside of the property let
procedure for yield:
Public Property Let Yield(ByRef NewYield As Double)
m_dYield = NewYield
m_bYieldSet = True
End Property

Thanks, Steve; I guess I'll convert the data elements to variants, since
the IsEmpty function will do what I want. Also, thanks for the
suggestion about Let/Get routine names.