ByRef or ByVal

  • Thread starter Thread starter Hei
  • Start date Start date
H

Hei

Hi,

i know the difference of ByRef and ByVal, in case if use byref or byval
don't affect the result which one should prefer? (less memory use, better
performance ....issue)

thx
 
Hei said:
i know the difference of ByRef and ByVal, in case if use byref or
byval don't affect the result which one should prefer? (less memory
use, better performance ....issue)
Click to expand...

My personal basic rule: If the procedure shouldn't change the passed value,
declare it ByVal, otherwise ByRef.

The "passed value" is the reference to an object if it is a reference type.
The "passed value" is the object itself if it is a value type.
 
* "Hei said:
i know the difference of ByRef and ByVal, in case if use byref or byval
don't affect the result which one should prefer? (less memory use, better
performance ....issue)
Click to expand...

There _is_ a difference between 'ByVal' and 'ByRef'. In VB.NET, 'ByVal'
is used by default because it often makes more sense. 'ByRef' is only
relevant for reference types, if the _reference_ itself should be
changed by the procedure.
 
Herfried K. Wagner said:
There _is_ a difference between 'ByVal' and 'ByRef'. In VB.NET,
'ByVal' is used by default because it often makes more sense.
'ByRef' is only relevant for reference types, if the _reference_
itself should be changed by the procedure.
Click to expand...


Why do you think that ByRef is only relevant for reference types??
 
* "Armin Zingler said:
Why do you think that ByRef is only relevant for reference types??
Click to expand...

Maybe my bad skills in the English language caused the misinterpretation
on your side. If wanted to point out when 'ByRef' makes sense when used
with reference types.
 
Herfried K. Wagner said:
Maybe my bad skills in the English language
Click to expand...

haha.. ;)
caused the
misinterpretation on your side. If wanted to point out when 'ByRef'
makes sense when used with reference types.
Click to expand...

I still don't understand - but, no need for an explanation. We know what
byval/byref do. ;-)
 
Hei,
i know the difference of ByRef and ByVal, in case if use byref or byval
don't affect the result which one should prefer? (less memory use, better
performance ....issue)
Click to expand...
Are you sure you know the difference? ;-)

ByVal & ByRef Parameters are independent of Reference & Value Types. All
parameters by default are passed ByVal, you should only pass a parameter
ByRef when you have to, which is when you need to modify the callers
variable.

Less memory use & better performance should not be a factor in choosing
ByVal & ByRef. The only time to consider ByRef for less memory & performance
is when passing large structures (structures as in defined with the
Structure keyword), however structures should never be large!

Structure Usage Guidelines.
http://msdn.microsoft.com/library/d...genref/html/cpconvaluetypeusageguidelines.asp

A Reference Type is an object that exists on the heap. If I have a variable
that is a reference type and assign the variable to another variable. Both
variables will be pointing to the same object on the heap.

Dim x As Person
x = New Person()
Dim y As Person
y = x

Both x & y are the exact same Person object on the heap.

A Value Type does not live on the Heap. If I have a value type variable and
I assign it to another variable, a copy of the value is made.

Dim x As Integer
x = 100
Dim y As Integer
y = x

Although both x & y have the value 100, they are physically different values
as a copy was made.

Now when you pass a variable to a ByVal parameter a copy of the variable is
made. So for a Reference Type a copy of the reference is made, which means
there is still only one object on the heap & two references to that object.
For a Value Type a copy of the value is made.

When you pass a variable to a ByRef parameter a reference to that variable
is made. So for a Reference Type you have a reference to a reference to the
object, for a Value Type you have a reference to the value.

Remember ByVal & ByRef are how parameters are passed. Reference & Value
Types are how quantities are stored.

Hope this helps
Jay
 
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