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
  }