The ref keyword

You use the ref keyword in the following contexts:

• In a method signature and in a method call, to pass an argument to a method by reference.

public void M(ref int refParameter)
{
    refParameter += 42;
}

• In a method signature, to return a value to the caller by reference. For more information, see ref return.

public ref int RefMax(ref int left, ref int right)
{
    if (left > right)
    {
        return ref left;
    }
    else
    {
        return ref right;
    }
}

• In a declaration of a local variable, to declare a reference variable.

public void M2(int variable)
{
    ref int aliasOfvariable = ref variable;
}

• As the part of a conditional ref expression or a ref assignment operator.

public ref int RefMaxConditions(ref int left, ref int right)
{
    ref int returnValue = ref left > right ? ref left : ref right;
    return ref returnValue;
}

• In a struct declaration, to declare a ref struct. For more information, see the ref structure types article.

public ref struct CustomRef
{
    public ReadOnlySpan<int> Inputs;
    public ReadOnlySpan<int> Outputs;
}

• In a ref struct definition, to declare a ref field. For more information, see the ref fields section of the ref structure types article.

public ref struct RefFieldExample
{
    private ref int number;
}

• In a generic type declaration to specify that a type parameter allows ref struct types.

class RefStructGeneric<T, S>
    where T : allows ref struct
    where S : T
{
    // etc
}