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Professional Visual Basic 2012 and .NET 4.5 Programming by Todd Herman, Gastón Hillar, David McCarter, Rob Windsor, Billy Hollis, Bill Sheldon

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Parameter Passing

When an object's methods or an assembly's procedures and methods are called, it's often appropriate to provide input for the data to be operated on by the code. The values are referred to as parameters, and any object can be passed as a parameter to a Function or Sub.

When passing parameters, be aware of whether the parameter is being passed “by value” (ByVal) or “by reference” (ByRef). Passing a parameter by value means that if the value of that variable is changed, then when the Function/Sub returns, the system automatically restores that variable to the value it had before the call. Passing a parameter by reference means that if changes are made to the value of a variable, then these changes affect the actual variable and, therefore, are still present when the variable returns.

This is where it gets a little challenging for new Visual Basic developers. Under .NET, passing a parameter by value indicates only how the top-level reference (the portion of the variable on the stack) for that object is passed. Sometimes referred to as a shallow copy operation, the system copies only the top-level reference value for an object passed by value, and it is only this reference which is protected. This is important to remember because it means that referenced memory is not protected.

When you pass an integer by value, if the program changes the value of the integer, then your original value is restored. Conversely, if you pass a reference type, then only the location of ...

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