C# arrays of structs and assignment performance

Question

Suppose I have this code:

struct Normal
{
    public float x;
    public float y;
}

class NormalContainer
{
   public Normal[] Normals
   {
       get; set;
   }
}

class Main
{
     void Run( NormalContainer container )
     {
         Normal[] normals = container.Normals // 1 - see below
         normals[5].x = 4;                    // 3 - see below
         container.Normals = normals;         // 2 - see below
     }
}

Does (1) create a copy of the array or is this a reference to the memory occupied by the array? What about (2) ?

Thanks

This would be an excellent time to fire up the debugger and trace those statements - you can then see if the code makes any difference to what's inside the passed object or not. — JTeagle
– JTeagle, Commented Mar 14, 2012 at 16:01

BrokenGlass · Accepted Answer · 2012-03-14 15:59:18Z

3

Array is a reference type, so you are just copying the reference to the array instance.

answered Mar 14, 2012 at 15:59

BrokenGlass

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Comments

JaredPar · Accepted Answer · 2012-03-14 15:59:17Z

2

An array in C# is a reference type. Items like assignment create copies of the reference vs. the value. At the end of (1) you end up with a local reference to the array stored in container

Note: In C# it's more proper to say "reference to the object" vs. "reference to the memory"

answered Mar 14, 2012 at 15:59

JaredPar

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Comments

Saeb Amini · Accepted Answer · 2012-03-14 16:04:12Z

1

(1) copies the array's reference

(2) same

Array variables are reference types, regardless of their underlying element type, so whenever you assign an array variable to another, you are just copying the reference.

answered Mar 14, 2012 at 16:04

Saeb Amini

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2 Comments

sirival Over a year ago

So what happens on (3) ? If the array is a reference then if I do normals[5].x = 4 does that change the value in container.Normals before line (2) ? And if yes then line (2) is unnecessary correct?

sirival Over a year ago

Nevermind I sat down and wrote my example... This is exactly what happens.. Thank you!

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