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I am creating a VECTOR object like so, but I am initializing it in the constructor:

public VECTOR position { get; private set; }

I am doing this operation: 

position.x += 2;

VECTOR has a variable x defined as: 

public double x { get; set; }

I get the error when I do the +=2 operation that says:

Cannot modify the return value of 'Projectile.position' because it is not a variable

I want to be able to modify the position vector in the current class, and I want it to be accessible but not modifiable in other classes.

Drew Kennedy
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Anon E. Muss
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    Please put the class for Vector. – Dr. Stitch Feb 04 '16 at 23:41
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    I'm guessing Vector is a struct. Make it a class. – Andy Feb 04 '16 at 23:41
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    `x` isn't a variable, it's a property. Also, you haven't really given enough information. You should consider posting your definition of `VECTOR`. Finally, all caps in a class name goes against standard C# naming conventions. `Vector` would be expected by most C# developers, as would `Position`. – Kenneth K. Feb 04 '16 at 23:47
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    Please provide a [mcve]. – Enigmativity Feb 04 '16 at 23:50
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    A quick google on the error message gave me [this question](http://stackoverflow.com/questions/1747654/cannot-modify-the-return-value-error-c-sharp) – Setsu Feb 04 '16 at 23:52

2 Answers2

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Probably, your problem is with the Vector class actually being a struct. Assume you have the following declarations:

public class Projectile
{
    public VECTOR position { get; private set; }        

    public Projectile()
    {
        position = new VECTOR();
    }
}

public struct VECTOR 
{
    public double x {get; set;} 
}

You cant edit properties of the position property directly because you are accessing a copy of that field (explained here).

If you don`t want to convert your VECTOR into a class you can add a method that updates the position of your projectile:

public void UpdatePosition(double newX)
{       
    var newPosition = position;
    newPosition.x = newX;

    position = newPosition;
}

That will create a copy of the position, then update its x property and override the stored position. And the usage would be similar to this:

p.UpdatePosition(p.position.x + 2);
Community
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JleruOHeP
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-1

Expose the X property (and others) of VECTOR in a class.

public class myObject {
private VECTOR position;
public double X { get{return position.x;}set{position.x=value;}}
}

Usage example: myObject.X += 2;

James
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