Article ID: 138535 - View products that this article applies to.
This article was previously published under Q138535
If you pass a parameter to a function or sub procedure by reference, the type of the actual parameter passed and the corresponding function argument must match. Otherwise, you will get a "ByRef argument type mismatch" error.
The reason types have to match with ByRef parameters is that the called procedure is working on the original outside variable through a reference pointer. In the following step-by-step example, if the procedure thinks it is modifying a variant but the outside variable is really a control, the data will probably be ruined.
If something is passed by value, Visual Basic can do automatic type conversion. When you pass by value, the inside procedure is working on a copy and can therefore modify it in any way, such as converting the passed object to a temporary Variant and working on that.
This applies to simple built-in types as well as objects. Problems like this are easier to understand and debug if you set Option Explicit and declare every variable type explicitly.
Article ID: 138535 - Last Review: January 8, 2003 - Revision: 1.1
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