How to 'do' ByVal in C#

c# vb.net byref byval
Jouke van der Maas picture Jouke van der Maas · Jun 14, 2010 · Viewed 40.8k times · Source

As I understand it, C# passes parameters into methods by reference. In VB.NET, you can specify this with ByVal and ByRef. The default is ByVal.

Is this for compatibility with Visual Basic 6.0, or is it just random? Also, how can I specify what to use in C#? I kind of like the idea of passing parameters by value.

Answer

Marc Gravell picture Marc Gravell · Jun 14, 2010

Parameters in C# are, by default passed by value. There is no modifier to make this explicit, but if you add ref / out the parameter is by-reference.

The usual confusion here is the difference between:

  • passing a value-type by value (changes to the value-type are not visible to the caller, but value-types should ideally be immutable anyway)
  • passing a value-type by reference (changes to the value-type are visible to the caller, but value-types should ideally be immutable anyway - so important I'll say it twice ;p)
  • passing a reference by value (changes to fields/properties of the ref-type are visible to the caller, but reassigning the ref-type to a new/different object is not visible)
  • passing a reference by reference (changes to fields/properties, and reassigning the reference are visible to the caller)

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