Reference Types and Value Types

[daniel]

This is a pretty basic-level question, but I'd really like to know, so
thanks for any help or pointers you can provide (like what I would
google for ;o)

Suppose:

<code>

myFunc()
{
SomeType myType = new SomeType;
Console.Write(m yType.MyPropert y);
bool whatever = myOtherFunc(myT ype);
}

myOtherfunc(Som eType passedType)
{
Console.Write(m yType.ToString( ))
return true;
}

</code>

My question: since myType is a reference type, only one instance of this
object is ever created in memory, right? The Lead Software Architect
here (C++, no C# experience) was telling me about passing by reference--
is this implicitly done by reference types in C#? Also, could I pass by
value? Why would I want to?

All these questions are asked under the auspices of least amount of
overhead. My primary concern is good coding practices (and learning).

Thank you,
-daniel

[Lateralus [MCAD]]

Re: Reference Types and Value Types

daniel,
To my knowledge you can't pass a "reference" type by value if you wanted
to. It is automatically passed by reference. If you have a value type and
you want to maintain it's value across method calls, you need to pass it by
reference.

example should print out 12:

private void Test()
{
int index = 0;
Test2(ref index);
Console.Write(i ndex.ToString() );
}

private void Test2(ref index)
{
index = 12;
}

--
Lateralus [MCAD]


"daniel" <user@example.c om> wrote in message
news:%23kBDwNTk EHA.3724@TK2MSF TNGP11.phx.gbl. ..[color=blue]
> This is a pretty basic-level question, but I'd really like to know, so
> thanks for any help or pointers you can provide (like what I would google
> for ;o)
>
> Suppose:
>
> <code>
>
> myFunc()
> {
> SomeType myType = new SomeType;
> Console.Write(m yType.MyPropert y);
> bool whatever = myOtherFunc(myT ype);
> }
>
> myOtherfunc(Som eType passedType)
> {
> Console.Write(m yType.ToString( ))
> return true;
> }
>
> </code>
>
> My question: since myType is a reference type, only one instance of this
> object is ever created in memory, right? The Lead Software Architect here
> (C++, no C# experience) was telling me about passing by reference--
> is this implicitly done by reference types in C#? Also, could I pass by
> value? Why would I want to?
>
> All these questions are asked under the auspices of least amount of
> overhead. My primary concern is good coding practices (and learning).
>
> Thank you,
> -daniel[/color]

[daniel]

Re: Reference Types and Value Types

Ahh, thank you Lateralus for the quick reply. I have a quick follow up
question, though:

If a reference type is always passed by reference, then (while stupid
and messy):

<code>
// with a return type this time!
void func1()
{
SomeType myType = new myType();
func2(myType);
}
void func2(SomeType myType)
{
func3(mytype);
}
void func3(SomeType myType)
{
Console.Write(m yType.ToString( ));
}
</code>

will not cause a substantial amount of increased overhead at all (other
than variables on the stack), because only one object is every created.


Thanks,
-daniel



Lateralus [MCAD] wrote:
[color=blue]
> daniel,
> To my knowledge you can't pass a "reference" type by value if you wanted
> to. It is automatically passed by reference. If you have a value type and
> you want to maintain it's value across method calls, you need to pass it by
> reference.
>
> example should print out 12:
>
> private void Test()
> {
> int index = 0;
> Test2(ref index);
> Console.Write(i ndex.ToString() );
> }
>
> private void Test2(ref index)
> {
> index = 12;
> }
>[/color]

[Jay B. Harlow [MVP - Outlook]]

Re: Reference Types and Value Types

Daniel,
For information on reference types & value types along with passing by value
& passing by reference see:

http://www.yoda.arachsys.com/csharp/parameters.html

Hope this helps
Jay

"daniel" <user@example.c om> wrote in message
news:%23kBDwNTk EHA.3724@TK2MSF TNGP11.phx.gbl. ..[color=blue]
> This is a pretty basic-level question, but I'd really like to know, so
> thanks for any help or pointers you can provide (like what I would google
> for ;o)
>
> Suppose:
>
> <code>
>
> myFunc()
> {
> SomeType myType = new SomeType;
> Console.Write(m yType.MyPropert y);
> bool whatever = myOtherFunc(myT ype);
> }
>
> myOtherfunc(Som eType passedType)
> {
> Console.Write(m yType.ToString( ))
> return true;
> }
>
> </code>
>
> My question: since myType is a reference type, only one instance of this
> object is ever created in memory, right? The Lead Software Architect here
> (C++, no C# experience) was telling me about passing by reference--
> is this implicitly done by reference types in C#? Also, could I pass by
> value? Why would I want to?
>
> All these questions are asked under the auspices of least amount of
> overhead. My primary concern is good coding practices (and learning).
>
> Thank you,
> -daniel[/color]

[Lateralus [MCAD]]

Re: Reference Types and Value Types

daniel,
That is correct. There is only one storage location of the object. The
variables all just point to the same object.

--
Lateralus [MCAD]


"daniel" <user@example.c om> wrote in message
news:OfNECeTkEH A.3724@TK2MSFTN GP11.phx.gbl...[color=blue]
> Ahh, thank you Lateralus for the quick reply. I have a quick follow up
> question, though:
>
> If a reference type is always passed by reference, then (while stupid and
> messy):
>
> <code>
> // with a return type this time!
> void func1()
> {
> SomeType myType = new myType();
> func2(myType);
> }
> void func2(SomeType myType)
> {
> func3(mytype);
> }
> void func3(SomeType myType)
> {
> Console.Write(m yType.ToString( ));
> }
> </code>
>
> will not cause a substantial amount of increased overhead at all (other
> than variables on the stack), because only one object is every created.
>
>
> Thanks,
> -daniel
>
>
>
> Lateralus [MCAD] wrote:
>[color=green]
>> daniel,
>> To my knowledge you can't pass a "reference" type by value if you
>> wanted to. It is automatically passed by reference. If you have a value
>> type and you want to maintain it's value across method calls, you need to
>> pass it by reference.
>>
>> example should print out 12:
>>
>> private void Test()
>> {
>> int index = 0;
>> Test2(ref index);
>> Console.Write(i ndex.ToString() );
>> }
>>
>> private void Test2(ref index)
>> {
>> index = 12;
>> }
>>[/color][/color]

[Jeff Louie]

Re: Reference Types and Value Types

Daniel.... By default all parameters in C# are passed by value, but you
cannot
pass an actual object as a parameter. You can only a pass a reference
to an
object as a parameter. So, by default, in C# you actually pass a
reference by
value as a parameter. This is very confusing to C++ coders who assume
this
is the equivalent of C++ pass by reference. It is not. Although the
behavior is
_similar_ to C++ pass by reference, it is not identical. So C++ coders
need to
understand first that although objects use value semantics in C++,
objects in
C# use reference semantics. For instance, RefVariableA= RefVariableB
does
not call a copy constructor in C#, it simply assigns RefVariableA to
"point" to
the same object "pointed" to by RefVariableB. In C#, you pass a
reference to
an an object by value so that a copy of the reference goes on the stack.
The
object is not copied. You can touch and modify the object using the
reference
within the method, but if you reassign the reference within the method
there
are no side effects outside of the method. Of course, this does not
apply if
you override the default behaviour and explicitly pass a parameter by
reference. So to summarize, since objects in C++ use value semantics and
objects in C# use reference semantics, the concept of "pass by
reference" has
a very different meaning in C++ and C#.

Regards,
Jeff[color=blue]
>My question: since myType is a reference type, only one instance of[/color]
this
object is ever created in memory, right? The Lead Software Architect
here (C++, no C# experience) was telling me about passing by reference--
is this implicitly done by reference types in C#? Also, could I pass by
value?<

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[daniel]

Re: Reference Types and Value Types

Thank you Lateralus, Jay and Jeff.

[Jon Skeet [C# MVP]]

Re: Reference Types and Value Types

<"Lateralus [MCAD]" <dnorm252_at_ya hoo.com>> wrote:[color=blue]
> To my knowledge you can't pass a "reference" type by value if you wanted
> to. It is automatically passed by reference.[/color]

No. The reference is passed by value, which is quite different.

See http://www.pobox.com/~skeet/csharp/parameters.html

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too

[Patty O'Dors]

RE: Reference Types and Value Types

You can't pass by value in C#, not unless the type is a value type, like
something that is declared 'struct' rather than 'class', or a basic variable
like int, byte etc.
There's no reason why you'd want to, if you did, then that'd be tantamount
to trying to do the garbage collector's work for it, and it was designed to
be global and operate off its own bat.
So just don't bother about the memory - just make it as OO as possible.

"daniel" wrote:
[color=blue]
> This is a pretty basic-level question, but I'd really like to know, so
> thanks for any help or pointers you can provide (like what I would
> google for ;o)
>
> Suppose:
>
> <code>
>
> myFunc()
> {
> SomeType myType = new SomeType;
> Console.Write(m yType.MyPropert y);
> bool whatever = myOtherFunc(myT ype);
> }
>
> myOtherfunc(Som eType passedType)
> {
> Console.Write(m yType.ToString( ))
> return true;
> }
>
> </code>
>
> My question: since myType is a reference type, only one instance of this
> object is ever created in memory, right? The Lead Software Architect
> here (C++, no C# experience) was telling me about passing by reference--
> is this implicitly done by reference types in C#? Also, could I pass by
> value? Why would I want to?
>
> All these questions are asked under the auspices of least amount of
> overhead. My primary concern is good coding practices (and learning).
>
> Thank you,
> -daniel
>[/color]

[Jon Skeet [C# MVP]]

RE: Reference Types and Value Types

Patty O'Dors <PattyODors@dis cussions.micros oft.com> wrote:[color=blue]
> You can't pass by value in C#, not unless the type is a value type, like
> something that is declared 'struct' rather than 'class', or a basic variable
> like int, byte etc.[/color]

Not true. Everything is passed by value by default - whether the value
is a struct or a reference. You can't pass an actual *object* either by
reference or by value.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too

[Champika Nirosh]

Re: Reference Types and Value Types

How about assigning a deep clone of the reference type object to a new
object of same type.. at the method..

Nirosh.

"Lateralus [MCAD]" <dnorm252_at_ya hoo.com> wrote in message
news:eLFDzjVkEH A.3968@TK2MSFTN GP11.phx.gbl...[color=blue]
> daniel,
> That is correct. There is only one storage location of the object. The
> variables all just point to the same object.
>
> --
> Lateralus [MCAD]
>
>
> "daniel" <user@example.c om> wrote in message
> news:OfNECeTkEH A.3724@TK2MSFTN GP11.phx.gbl...[color=green]
> > Ahh, thank you Lateralus for the quick reply. I have a quick follow up
> > question, though:
> >
> > If a reference type is always passed by reference, then (while stupid[/color][/color]
and[color=blue][color=green]
> > messy):
> >
> > <code>
> > // with a return type this time!
> > void func1()
> > {
> > SomeType myType = new myType();
> > func2(myType);
> > }
> > void func2(SomeType myType)
> > {
> > func3(mytype);
> > }
> > void func3(SomeType myType)
> > {
> > Console.Write(m yType.ToString( ));
> > }
> > </code>
> >
> > will not cause a substantial amount of increased overhead at all (other
> > than variables on the stack), because only one object is every created.
> >
> >
> > Thanks,
> > -daniel
> >
> >
> >
> > Lateralus [MCAD] wrote:
> >[color=darkred]
> >> daniel,
> >> To my knowledge you can't pass a "reference" type by value if you
> >> wanted to. It is automatically passed by reference. If you have a value
> >> type and you want to maintain it's value across method calls, you need[/color][/color][/color]
to[color=blue][color=green][color=darkred]
> >> pass it by reference.
> >>
> >> example should print out 12:
> >>
> >> private void Test()
> >> {
> >> int index = 0;
> >> Test2(ref index);
> >> Console.Write(i ndex.ToString() );
> >> }
> >>
> >> private void Test2(ref index)
> >> {
> >> index = 12;
> >> }
> >>[/color][/color]
>
>[/color]

[Champika Nirosh]

Re: Reference Types and Value Types


"Jon Skeet [C# MVP]" <skeet@pobox.co m> wrote in message
news:MPG.1ba27a 49964d884998b34 0@msnews.micros oft.com...[color=blue]
> Patty O'Dors <PattyODors@dis cussions.micros oft.com> wrote:[color=green]
> > You can't pass by value in C#, not unless the type is a value type, like
> > something that is declared 'struct' rather than 'class', or a basic[/color][/color]
variable[color=blue][color=green]
> > like int, byte etc.[/color]
>
> Not true. Everything is passed by value by default - whether the value
> is a struct or a reference. You can't pass an actual *object* either by
> reference or by value.[/color]

"Everything " are u sure....?????
[color=blue]
> --
> Jon Skeet - <skeet@pobox.co m>
> http://www.pobox.com/~skeet
> If replying to the group, please do not mail me too[/color]

[Jon Skeet [C# MVP]]

Re: Reference Types and Value Types

Champika Nirosh <test@test.lk > wrote:[color=blue][color=green]
> > Not true. Everything is passed by value by default - whether the value
> > is a struct or a reference. You can't pass an actual *object* either by
> > reference or by value.[/color]
>
> "Everything " are u sure....?????[/color]

Absolutely. See http://www.pobox.com/~skeet/csharp/parameters.html

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too

[Champika Nirosh]

Re: Reference Types and Value Types

Hi Jon,

I think it is not a fair comment...

"Everything is passed by value by default"

Instead.. What you would said is.. reference of the reference type variable
is passed by its' value.. or object references are passed by value by
default..

You statement is misleading... One might take it as .. object also passed by
its' value.. what happen actaully is since reference type cannot passed by
value even though you try they passes their reference..

Nirosh.

"Jon Skeet [C# MVP]" <skeet@pobox.co m> wrote in message
news:MPG.1bd441 4677f9299a98b64 c@msnews.micros oft.com...[color=blue]
> Champika Nirosh <test@test.lk > wrote:[color=green][color=darkred]
> > > Not true. Everything is passed by value by default - whether the value
> > > is a struct or a reference. You can't pass an actual *object* either[/color][/color][/color]
by[color=blue][color=green][color=darkred]
> > > reference or by value.[/color]
> >
> > "Everything " are u sure....?????[/color]
>
> Absolutely. See http://www.pobox.com/~skeet/csharp/parameters.html
>
> --
> Jon Skeet - <skeet@pobox.co m>
> http://www.pobox.com/~skeet
> If replying to the group, please do not mail me too[/color]

[Jon Skeet [C# MVP]]

Re: Reference Types and Value Types

Champika Nirosh <test@test.lk > wrote:[color=blue]
> I think it is not a fair comment...
>
> "Everything is passed by value by default"[/color]

It's a true comment. The only things which can be passed are value
types and references. Both of those are passed by value by default.
[color=blue]
> Instead.. What you would said is.. reference of the reference type variable
> is passed by its' value.. or object references are passed by value by
> default..[/color]

But that's all that *can* be passed. Note that it's not the reference
of the reference type variable - it's the *value* of a reference type
variable, and that value is a reference.
[color=blue]
> You statement is misleading... One might take it as .. object also passed by
> its' value.. what happen actaully is since reference type cannot passed by
> value even though you try they passes their reference..[/color]

If that's all I'd said, you'd be right. However, look at what I *did*
say:

<quote>
Not true. Everything is passed by value by default - whether the value
is a struct or a reference. You can't pass an actual *object* either by
reference or by value.
</quote>

Now, how can *that* be taken as "object also passed by its value"?

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too