When is the VBA CVar function actually useful?
2
VBA implicitly converts values to Variant as needed, so what would be a use case of the CVar function? In the example given in the documentation, the call to CVar is obviously redundant.
To be precise, I am looking for a concrete, minimal VBA code example, which
- compiles, but
- won't compile (or produce a different output) when (only!)
CVar(...some expression...)is replaced by...some expression....
I haven't been able to find such an example, but maybe the someone else can.
vba language-lawyer
asked Nov 14 '18 at 9:59
Heinzi
122k38266403
add a comment |
2
VBA implicitly converts values to Variant as needed, so what would be a use case of the CVar function? In the example given in the documentation, the call to CVar is obviously redundant.
To be precise, I am looking for a concrete, minimal VBA code example, which
- compiles, but
- won't compile (or produce a different output) when (only!)
CVar(...some expression...)is replaced by...some expression....
I haven't been able to find such an example, but maybe the someone else can.
vba language-lawyer
asked Nov 14 '18 at 9:59
Heinzi
122k38266403
add a comment |
2
2
2
1
VBA implicitly converts values to Variant as needed, so what would be a use case of the CVar function? In the example given in the documentation, the call to CVar is obviously redundant.
To be precise, I am looking for a concrete, minimal VBA code example, which
- compiles, but
- won't compile (or produce a different output) when (only!)
CVar(...some expression...)is replaced by...some expression....
I haven't been able to find such an example, but maybe the someone else can.
vba language-lawyer
asked Nov 14 '18 at 9:59
Heinzi
122k38266403
VBA implicitly converts values to Variant as needed, so what would be a use case of the CVar function? In the example given in the documentation, the call to CVar is obviously redundant.
To be precise, I am looking for a concrete, minimal VBA code example, which
- compiles, but
- won't compile (or produce a different output) when (only!)
CVar(...some expression...)is replaced by...some expression....
I haven't been able to find such an example, but maybe the someone else can.
vba language-lawyer
vba language-lawyer
asked Nov 14 '18 at 9:59
Heinzi
122k38266403
asked Nov 14 '18 at 9:59
Heinzi
122k38266403
asked Nov 14 '18 at 9:59
Heinzi
122k38266403
asked Nov 14 '18 at 9:59
Heinzi
122k38266403
asked Nov 14 '18 at 9:59
Heinzi
122k38266403
122k38266403
add a comment |
add a comment |
2 Answers
2
active
oldest
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2
I cannot think about a real life usage for the following, but at least it shows that you could need the function:
Sub test()
Dim myInt As Integer
myInt = 2
' The following call will throw a runtime error in testSub
Call testSub(myInt)
' That's okay
Call testSub(CVar(myInt))
End Sub
Sub testSub(ByRef p As Variant)
Debug.Print "P: " & VarType(p)
p = "ABC"
End Sub
answered Nov 14 '18 at 10:09
FunThomas
4,5311523
1
A good one, I expected it to raise a compile time byref mismatch which it does not. But this kind of problems are usually worked around withCall testSub((myInt)).
– GSerg
Nov 14 '18 at 10:22
@GSerg: Interesting. That means that(myInt)returns aVariant...
– FunThomas
Nov 14 '18 at 10:32
1
In your examplemyIntis also passed asVariant, but withVT_BYREF. The()remove that flag. It's an interesting subject with interesting results, e.g. see stackoverflow.com/q/52686198/11683.
– GSerg
Nov 14 '18 at 10:35
@GSerg: Just for curiosity: Do you know any way to read the VT-Flags within VBA?
– FunThomas
Nov 14 '18 at 10:47
Yes, read the first two bytes starting atVarPtr(that_variable). An example: stackoverflow.com/a/43554246/11683
– GSerg
Nov 14 '18 at 10:49
add a comment |
2
Not sure if that qualifies, but the only thing I can think of is the interaction with As Any in Declare.
Private Declare PtrSafe Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
(Destination As Any, source As Any, ByVal Length As Long)
Sub Test()
Dim source As Long, dest As Long
source = 42
CopyMemory dest, CVar(source), 4
MsgBox dest
CopyMemory dest, source, 4
MsgBox dest
End Sub
answered Nov 14 '18 at 10:57
GSerg
58.9k14101219
Nice one! I thought about overloading, but rejected the idea, since VBA itself does not support it, and completely forgot about overload consuming withAs Any.
– Heinzi
Nov 14 '18 at 13:07
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
2
I cannot think about a real life usage for the following, but at least it shows that you could need the function:
Sub test()
Dim myInt As Integer
myInt = 2
' The following call will throw a runtime error in testSub
Call testSub(myInt)
' That's okay
Call testSub(CVar(myInt))
End Sub
Sub testSub(ByRef p As Variant)
Debug.Print "P: " & VarType(p)
p = "ABC"
End Sub
answered Nov 14 '18 at 10:09
FunThomas
4,5311523
1
A good one, I expected it to raise a compile time byref mismatch which it does not. But this kind of problems are usually worked around withCall testSub((myInt)).
– GSerg
Nov 14 '18 at 10:22
@GSerg: Interesting. That means that(myInt)returns aVariant...
– FunThomas
Nov 14 '18 at 10:32
1
In your examplemyIntis also passed asVariant, but withVT_BYREF. The()remove that flag. It's an interesting subject with interesting results, e.g. see stackoverflow.com/q/52686198/11683.
– GSerg
Nov 14 '18 at 10:35
@GSerg: Just for curiosity: Do you know any way to read the VT-Flags within VBA?
– FunThomas
Nov 14 '18 at 10:47
Yes, read the first two bytes starting atVarPtr(that_variable). An example: stackoverflow.com/a/43554246/11683
– GSerg
Nov 14 '18 at 10:49
add a comment |
2
I cannot think about a real life usage for the following, but at least it shows that you could need the function:
Sub test()
Dim myInt As Integer
myInt = 2
' The following call will throw a runtime error in testSub
Call testSub(myInt)
' That's okay
Call testSub(CVar(myInt))
End Sub
Sub testSub(ByRef p As Variant)
Debug.Print "P: " & VarType(p)
p = "ABC"
End Sub
answered Nov 14 '18 at 10:09
FunThomas
4,5311523
1
A good one, I expected it to raise a compile time byref mismatch which it does not. But this kind of problems are usually worked around withCall testSub((myInt)).
– GSerg
Nov 14 '18 at 10:22
@GSerg: Interesting. That means that(myInt)returns aVariant...
– FunThomas
Nov 14 '18 at 10:32
1
In your examplemyIntis also passed asVariant, but withVT_BYREF. The()remove that flag. It's an interesting subject with interesting results, e.g. see stackoverflow.com/q/52686198/11683.
– GSerg
Nov 14 '18 at 10:35
@GSerg: Just for curiosity: Do you know any way to read the VT-Flags within VBA?
– FunThomas
Nov 14 '18 at 10:47
Yes, read the first two bytes starting atVarPtr(that_variable). An example: stackoverflow.com/a/43554246/11683
– GSerg
Nov 14 '18 at 10:49
add a comment |
2
2
2
I cannot think about a real life usage for the following, but at least it shows that you could need the function:
Sub test()
Dim myInt As Integer
myInt = 2
' The following call will throw a runtime error in testSub
Call testSub(myInt)
' That's okay
Call testSub(CVar(myInt))
End Sub
Sub testSub(ByRef p As Variant)
Debug.Print "P: " & VarType(p)
p = "ABC"
End Sub
answered Nov 14 '18 at 10:09
FunThomas
4,5311523
I cannot think about a real life usage for the following, but at least it shows that you could need the function:
Sub test()
Dim myInt As Integer
myInt = 2
' The following call will throw a runtime error in testSub
Call testSub(myInt)
' That's okay
Call testSub(CVar(myInt))
End Sub
Sub testSub(ByRef p As Variant)
Debug.Print "P: " & VarType(p)
p = "ABC"
End Sub
answered Nov 14 '18 at 10:09
FunThomas
4,5311523
answered Nov 14 '18 at 10:09
FunThomas
4,5311523
answered Nov 14 '18 at 10:09
FunThomas
4,5311523
answered Nov 14 '18 at 10:09
FunThomas
4,5311523
4,5311523
1
A good one, I expected it to raise a compile time byref mismatch which it does not. But this kind of problems are usually worked around withCall testSub((myInt)).
– GSerg
Nov 14 '18 at 10:22
@GSerg: Interesting. That means that(myInt)returns aVariant...
– FunThomas
Nov 14 '18 at 10:32
1
In your examplemyIntis also passed asVariant, but withVT_BYREF. The()remove that flag. It's an interesting subject with interesting results, e.g. see stackoverflow.com/q/52686198/11683.
– GSerg
Nov 14 '18 at 10:35
@GSerg: Just for curiosity: Do you know any way to read the VT-Flags within VBA?
– FunThomas
Nov 14 '18 at 10:47
Yes, read the first two bytes starting atVarPtr(that_variable). An example: stackoverflow.com/a/43554246/11683
– GSerg
Nov 14 '18 at 10:49
add a comment |
1
A good one, I expected it to raise a compile time byref mismatch which it does not. But this kind of problems are usually worked around withCall testSub((myInt)).
– GSerg
Nov 14 '18 at 10:22
@GSerg: Interesting. That means that(myInt)returns aVariant...
– FunThomas
Nov 14 '18 at 10:32
1
In your examplemyIntis also passed asVariant, but withVT_BYREF. The()remove that flag. It's an interesting subject with interesting results, e.g. see stackoverflow.com/q/52686198/11683.
– GSerg
Nov 14 '18 at 10:35
@GSerg: Just for curiosity: Do you know any way to read the VT-Flags within VBA?
– FunThomas
Nov 14 '18 at 10:47
Yes, read the first two bytes starting atVarPtr(that_variable). An example: stackoverflow.com/a/43554246/11683
– GSerg
Nov 14 '18 at 10:49
1
1
A good one, I expected it to raise a compile time byref mismatch which it does not. But this kind of problems are usually worked around with
Call testSub((myInt)).– GSerg
Nov 14 '18 at 10:22
A good one, I expected it to raise a compile time byref mismatch which it does not. But this kind of problems are usually worked around with
Call testSub((myInt)).– GSerg
Nov 14 '18 at 10:22
@GSerg: Interesting. That means that
(myInt) returns a Variant...– FunThomas
Nov 14 '18 at 10:32
@GSerg: Interesting. That means that
(myInt) returns a Variant...– FunThomas
Nov 14 '18 at 10:32
1
1
In your example
myInt is also passed as Variant, but with VT_BYREF. The () remove that flag. It's an interesting subject with interesting results, e.g. see stackoverflow.com/q/52686198/11683.– GSerg
Nov 14 '18 at 10:35
In your example
myInt is also passed as Variant, but with VT_BYREF. The () remove that flag. It's an interesting subject with interesting results, e.g. see stackoverflow.com/q/52686198/11683.– GSerg
Nov 14 '18 at 10:35
@GSerg: Just for curiosity: Do you know any way to read the VT-Flags within VBA?
– FunThomas
Nov 14 '18 at 10:47
@GSerg: Just for curiosity: Do you know any way to read the VT-Flags within VBA?
– FunThomas
Nov 14 '18 at 10:47
Yes, read the first two bytes starting at
VarPtr(that_variable). An example: stackoverflow.com/a/43554246/11683– GSerg
Nov 14 '18 at 10:49
Yes, read the first two bytes starting at
VarPtr(that_variable). An example: stackoverflow.com/a/43554246/11683– GSerg
Nov 14 '18 at 10:49
add a comment |
2
Not sure if that qualifies, but the only thing I can think of is the interaction with As Any in Declare.
Private Declare PtrSafe Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
(Destination As Any, source As Any, ByVal Length As Long)
Sub Test()
Dim source As Long, dest As Long
source = 42
CopyMemory dest, CVar(source), 4
MsgBox dest
CopyMemory dest, source, 4
MsgBox dest
End Sub
answered Nov 14 '18 at 10:57
GSerg
58.9k14101219
Nice one! I thought about overloading, but rejected the idea, since VBA itself does not support it, and completely forgot about overload consuming withAs Any.
– Heinzi
Nov 14 '18 at 13:07
add a comment |
2
Not sure if that qualifies, but the only thing I can think of is the interaction with As Any in Declare.
Private Declare PtrSafe Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
(Destination As Any, source As Any, ByVal Length As Long)
Sub Test()
Dim source As Long, dest As Long
source = 42
CopyMemory dest, CVar(source), 4
MsgBox dest
CopyMemory dest, source, 4
MsgBox dest
End Sub
answered Nov 14 '18 at 10:57
GSerg
58.9k14101219
Nice one! I thought about overloading, but rejected the idea, since VBA itself does not support it, and completely forgot about overload consuming withAs Any.
– Heinzi
Nov 14 '18 at 13:07
add a comment |
2
2
2
Not sure if that qualifies, but the only thing I can think of is the interaction with As Any in Declare.
Private Declare PtrSafe Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
(Destination As Any, source As Any, ByVal Length As Long)
Sub Test()
Dim source As Long, dest As Long
source = 42
CopyMemory dest, CVar(source), 4
MsgBox dest
CopyMemory dest, source, 4
MsgBox dest
End Sub
answered Nov 14 '18 at 10:57
GSerg
58.9k14101219
Not sure if that qualifies, but the only thing I can think of is the interaction with As Any in Declare.
Private Declare PtrSafe Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" _
(Destination As Any, source As Any, ByVal Length As Long)
Sub Test()
Dim source As Long, dest As Long
source = 42
CopyMemory dest, CVar(source), 4
MsgBox dest
CopyMemory dest, source, 4
MsgBox dest
End Sub
answered Nov 14 '18 at 10:57
GSerg
58.9k14101219
answered Nov 14 '18 at 10:57
GSerg
58.9k14101219
answered Nov 14 '18 at 10:57
GSerg
58.9k14101219
answered Nov 14 '18 at 10:57
GSerg
58.9k14101219
58.9k14101219
Nice one! I thought about overloading, but rejected the idea, since VBA itself does not support it, and completely forgot about overload consuming withAs Any.
– Heinzi
Nov 14 '18 at 13:07
add a comment |
Nice one! I thought about overloading, but rejected the idea, since VBA itself does not support it, and completely forgot about overload consuming withAs Any.
– Heinzi
Nov 14 '18 at 13:07
Nice one! I thought about overloading, but rejected the idea, since VBA itself does not support it, and completely forgot about overload consuming with
As Any.– Heinzi
Nov 14 '18 at 13:07
Nice one! I thought about overloading, but rejected the idea, since VBA itself does not support it, and completely forgot about overload consuming with
As Any.– Heinzi
Nov 14 '18 at 13:07
add a comment |
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