Assign a variadic array of strings by reference in C#

Question

I have a class called Category that takes a variadic constructor. The arguments are strings.

class Category
{
    string[] definedSets;  // Sets supplied to the constructor

    public Category(params string[] specifiedSets)
    {
        definedSets = specifiedSets;
    }

etc.

A call to the constructor might look like Category myCat = new Category(myString1, myString2);

The problem is that I would like definedSets to change if the content of myString1 or myString2 changes. I tried definedSets = ref specifiedSets;, but I get an error The left hand side of a ref assignment must be a ref variable and I don't know how to resolve that.

Am I on the right track here? What do I do?

Answer 1

strings are immutable, and you can not change their value. Whenever you assign a new value it allocates new memory. It is not possible to refer to the same memory location every time.

I would suggest to use the StringBuilder class and change type of definedSets to StringBuilder,

public class Category
{
    StringBuilder[] definedSets;  // Sets supplied to the constructor

    public Category(StringBuilder specifiedSets)
    {
        this.definedSets = specifiedSets;
    }
}

Proof of concept: .NET Fiddle

Answer 2

Just pass a regular array instead:

var strings = new[] { myString1, myString2 };
new Category(strings);

Then keep the array and change its elements whenever you want.

Answer 3

For that to work, you would have to wrap the strings in a custom wrapper class:

public class StrWrapper
{
    public string Value {get; set;}
    public StrWrapper(string val) => Value = val;
}

You can pass the object reference around and change the string inside it at any time.

Also note that you cannot save a string ref: https://stackoverflow.com/a/2982037/1974021 So even if you could get the ctor to accept a (string ref)[] array, you could only use it then & there and not store it.