no compile error while type mismatch

i have a function:

MyFunction (Param1 as MyEnum) as Variant

While i call the function like this:
lsReturn = MyFunction("123")

MyEnum is a long and "123" is a literal string.

How come no compile error is prompt while compile and making a EXE?

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chnelsonAsked:
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Valliappan ANSenior Tech ConsultantCommented:
It is by design in MS way. Look at this link:

http://msdn.microsoft.com/library/devprods/vs6/vbasic/vbcon98/vbconpassingargumentstoprocedures.htm

There is a similar example, as you your case.

Cheers.
amebaCommented:
Note that you are passing parameter "123" ByVal.
You are not passing string variable, but calculated value.

Option Explicit
Private Enum MyEnum
    dsNoRecords = 123
    dsNothingSelected
    dsNormal
    dsModify
    dsAdd
End Enum

Private Sub Form_Click()
    Dim lsReturn As Variant, x As String
    x = "123"
    lsReturn = MyFunction(x)     ' type mismatch error
   
    lsReturn = MyFunction((x))   ' no error, you are passing value of x
   
    lsReturn = MyFunction(x * 1) ' no error, you are passing calculated value
   
End Sub

Private Function MyFunction(Param1 As MyEnum) As Variant
    Beep
End Function
amebaCommented:
If you pass parameter by value, VB compiler will insert converson function automatically.
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Valliappan ANSenior Tech ConsultantCommented:
A nice explanation by ameba. :)
chnelsonAuthor Commented:
ameba,

is it some way to disable that kind of auto convertion?

This kind of weak type checking is really dangerous which cause lots of run-time error before delopying the EXE to customers.
chnelsonAuthor Commented:
ameba,

is it some way to disable that kind of auto convertion?

This kind of weak type checking is really dangerous which cause lots of run-time error before delopying the EXE to customers.
amebaCommented:
>is it some way to disable that kind of auto convertion?

Type checking is present if you pass variable ByRef.

VB will do many things 'behind the scene' to allow easy and fast programming.  If you remove 'Option Explicit' you don't have to declare variables.

Of course this can be dangerous, many VB programmers asked for 'Option Strict' or 'Option Anal Strict' to disable those 'features'...

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chnelsonAuthor Commented:
oh...
i got it...
asking you for a comment ameba,
to enforce strong type checking,
is it a good way to use ByRef instead of ByVal?
the only side-effect i think is that the parameters (ByRef) may be modified accidentally...
amebaCommented:
>to enforce strong type checking,
>is it a good way to use ByRef instead of ByVal?

No, use ByVal if you need to pass parameter one-way [in]
use ByRef if you need to pass parameter two-way [in]+[out]

--
Please, maintain your old questions! You still have many opened questions.
chnelsonAuthor Commented:
thanks ameba, very clear explaination
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