Changing value of readonly array

Question

I have this jagged array in C#:

    private static readonly float[][] Numbers = {
    new float[]{ 0.3f, 0.4f, 0.5}};

How can I override the value?

public static void SetNewNumbers(float[][] num){
    Numbers = num;}

This is not working because of readonly,what should be added? ( I cant change anything about Numbers)

That is the point of `readonly`, so you can't assign new value to it. — Guru Stron, Feb 12 '21 at 09:56
If `num` has the same number of outermost elements as `Numbers`, you're OK (i.e. 1 element, in your example). Otherwise, you're out of luck: that's the point of `readonly` — canton7, Feb 12 '21 at 09:56
But in case if outer arrays have the same number of inner ones you can just reassign them one by one. — Guru Stron, Feb 12 '21 at 09:57
Thank you for answers. Yes, they are the same, just different float values. I cant change anything about Numbers. What I need is: If a certain criteria is met I want to override this values, but if later the criteria is not met anymore, I want to return to the default values set in Numbers — DD995, Feb 12 '21 at 10:06
It's readonly, therefore you can only assign it when you initialize it or in the constructor. If you want to change the values later, you should not make it readonly. What was the reason you put readonly there to begin with? Edit: You want if certain criteria is met, to go back to the default. In this case, maybe make two variables? One readonly which is the default, and another one which actually holds the current value, which is not readonly? — Rick, Feb 12 '21 at 10:13
Changing global values are rarely a good idea, it can very easily lead to code that is impossible to understand. It would be much better with a method that checks whatever criteria you have, and return one set of numbers or the other. — JonasH, Feb 12 '21 at 10:42
_"I cant change anything about Numbers"_ -- wouldn't changing it's value, as you seem to be asking how to do, be doing exactly that? Your question is unclear; it's not clear what it is you actually want to do, never mind what the actual constraints are. Note that in high-quality real-world code, not only would this field be `readonly`, but it would reference a read-only collection, not an array. There would literally be no way to modify any part of it, because any static field like this should be used _only_ for invariant data. What you're actually doing here? No one can tell. — Peter Duniho, Feb 12 '21 at 21:28

score 2 · Answer 1 · edited Feb 12 '21 at 10:38

here is the info you need:

In a field declaration, readonly indicates that assignment to the field can only occur as part of the declaration or in a constructor in the same class. A readonly field can be assigned and reassigned multiple times within the field declaration and constructor.

when you declare Numbers read only then this is not allowed

Numbers = num

coz you can not change the reference but you can modify the object...

so this is valid:

Numbers[0] = new[] {0.0f, 0.0f, 0.0f};
Numbers[0][1] = 1.0f;

score 1 · Answer 2 · answered Feb 12 '21 at 21:22

You can reassign each value in Numbers assuming the new array matches:

void ResetNumbers(float[][] num) {
    if (num.Length != Numbers.Length || num[0].Length != Numbers[0].Length)
        throw new ArgumentException($"{nameof(num)} dimensions incorrect");

    for (int j1 = 0; j1 < Numbers.Length; ++j1) {
        for (int j2 = 0; j2 < Numbers[j1].Length; ++j2) {
            Numbers[j1][j2] = num[j1][j2];
        }
    }
}

Changing value of readonly array

2 Answers2