public static class RectangleExtension
{
public static Rectangle Offseted(this Rectangle rect, int x, int y)
{
rect.X += x;
rect.Y += y;
return rect;
}
}
....
public void foo()
{
Rectangle rect;
rect = new Rectangle(0, 0, 20, 20);
Console.WriteLine("1: " + rect.X + "; " + rect.Y);
rect.Offseted(50, 50);
Console.WriteLine("2: " + rect.X + "; " + rect.Y);
rect = rect.Offseted(50, 50);
Console.WriteLine("3: " + rect.X + "; " + rect.Y);
}
Output:
1: 0; 0
2: 0; 0
3: 50; 50
What I expected:
1: 0; 0
2: 50; 50
why does rect.Offseted(50, 50) not modify the x and y of the rectangle in step 2?
What do I have to do with my RectangleExtension method to get my expected result?
The answer is: structs
are always passed by value in C#, and Rectangle in your case is a struct
, not a class
.
Try this:
public class A {
public int x;
}
public struct B {
public int x;
}
public static class Extension {
public static A Add(this A value) {
value.x += 1;
return value;
}
public static B Add(this B value) {
value.x += 1;
return value;
}
}
class Program {
static void Main(string[] args) {
A a = new A();
B b = new B();
Console.WriteLine("a=" + a.x);
Console.WriteLine("b=" + b.x);
a.Add();
b.Add();
Console.WriteLine("a=" + a.x); //a=1
Console.WriteLine("b=" + b.x); //b=0
Console.ReadLine();
}
}
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