#272 – Differences Between ref and out Parameters

Ref and out parameters in C# are implemented in the same way, in the compiled code.  In both cases, a parameter is passed by reference, giving the method called a chance to change the underlying value.

ref and out parameters different purposes:

  • ref parameters are for input/output – a value is passed into a method and a new value is passed out
  • out parameters are for output – a value is passed out of a method

The compiler enforces the following rules:

  • ref parameters
    • A value must be assigned to parameter before method is called
    • Parameter may be referenced inside method before being written to
    • Parameter may be written to before returning from method
  • out parameters
    • A value may be assigned before method is called (but cannot be used inside method)
    • Parameter may not be referenced inside method before being written to
    • Parameter must be written to before returning from method
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About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

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