Parameter modifiers
Apparence
ref
Pass a parameter by reference.
// 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");
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ref readonly
Pass a parameter by reference and make it readonly.
Useful when you have a big value type and you want to pass only its reference for performances reason, but you don't want it to be overwritten.
var bigStruct = new BigStruct("name");
Method(ref bigStruct);
void Method(ref readonly BigStruct bigStruct)
{
bigStruct = new BigStruct("new name"); // you can't assign a readonly variable
bigStruct.Name = "new name"; // you can modify the object properties
}
int[] array = [ 1, 2, 3, 4 ];
var bigStruct = new BigStruct(array);
ref readonly int element = ref bigStruct.GetElement(2); // 3
element = 5; // you can't assign a readonly variable
ref readonly int GetElement(int index) => ref data[index];
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If the variable is a readonly variable, you must use the in modifier while calling the method. |
in
Create a temporary variable for the argument and pass the argument by readonly reference.
var i = 10;
Method(in i); // in is optional in th calling method
void Method6(in int i) // readonly copy of the initial parameter
{
i = 5; // you can't assign a readonly variable
}
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out
Allow to initialize the parameter in the method.
Method5(out var j); // 5
void Method5(out int i) => i = 5;
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params
A parameter which allows a comma-separated list of arguments or a collection of arguments.
Method(1, 2, 3);
int[] a = [1, 2, 3];
Method(a);
void Method(params int[] integers)
{ }
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