Passing Struct by Ref via Class Constructor

[Danny Tan]

Hi folks,

I'm a newbie, trying to pick up C#. This is something, I'm currently working
on for my assignment.

I understand that struct is a "value type". And I'm trying to pass a struct
by reference while instantizing a new Class object.

I can't seems to be able to get it to work. Even after using "ref", it is
still "passed-by-value".

Where did I go wrong?

Regards,
Danny

-------------------------------------------

public struct Bin
{
int j, k;

public Bin(int i, int j)
{
// --- some codes
}
//--- some codes
}

public ClassA
{
Bin bin;

// --- constructor
public ClassA(ref Bin x)
{
bin = x;
}
// --- some codes to change the values of bin
}

public class DriverClass
{
static void Main()
{
Bin bin = new Bin(value1, value2)

// --- instantiate new object passing struct by reference
ClassA NewObject = new ClassA(ref bin);
}
}

 

[Jon Skeet [C# MVP]]

I'm a newbie, trying to pick up C#. This is something, I'm currently working
on for my assignment.

I understand that struct is a "value type". And I'm trying to pass a struct
by reference while instantizing a new Class object.

I can't seems to be able to get it to work. Even after using "ref", it is
still "passed-by-value".

No, it's passed by reference. However, when you assign to the bin
member variable, that assignment is done by value - and there's no way
of avoiding that.

It looks like you basically want reference semantics for Bin rather
than value semantics - so why not make Bin a class rather than a
struct? Alternatively, create a wrapper class for Bin which lets you
change the value within it.

 

[Marina]

In the context of the constructor, 'x' is byref. So anything you do to 'x'
will be reflected in the caller.

However, the line: bin=x

Just follows the regular rules with structs. It makes a copy of 'x' and
puts it in bin. 'x' is still by ref. But that doesn't mean that 'bin' is.
bin is a separate instance of the struct.

 

[Danny Tan]

Thanks for the time to answer my query!

Will do so.

 

[Danny Tan]

ic. Thanks for the info!

In the context of the constructor, 'x' is byref. So anything you do to 'x'
will be reflected in the caller.

However, the line: bin=x

Just follows the regular rules with structs. It makes a copy of 'x' and
puts it in bin. 'x' is still by ref. But that doesn't mean that 'bin'
is. bin is a separate instance of the struct.