Parameter modifiers

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ref

Pass a parameter by reference.

Cs.svg
// value type
var i = 10;
Method0(i);     // 10
Method1(ref i); // 11

void Method0(int i) => i++;     // pass the value type parameter by value (copy)
void Method1(ref int i) => i++; // pass the value type parameter by reference

// reference type
var item = new Item("init name");
Method2(item);     // init name
Method3(ref item); // new name 3

// pass the reference type parameter by value: the reference is passed by value (copy)
// if the parameter is overwritten (the copy of the reference is overwritten), it doesn't affect the initial object
void Method2(Item item) => item = new("new name 2");

// pass the reference type parameter by reference: the reference is passed by reference
// if the parameter is overwritten (the initial reference is overwritten), it does affect the initial object
void Method3(ref Item item) => item = new("new name 3");

ref readonly

Pass a parameter by reference and make it readonly.

Cs.svg
var item = new Item("name");
Method(ref item);

static void Method(ref readonly Item item)
{
    item = new Item("new name"); // you can't assign a readonly variable
    item.Name = "new name";      // you can modify the object properties
}

out

Allow to initialize the parameter in the method.

Cs.svg
Method5(out var j); // 5

void Method5(out int i) => i = 5;