Difference between ByVal and ByRef?

In Visual Basic .NET, developers have the flexibility to pass function arguments either by value or by reference, employing distinct passing mechanisms to govern the interaction between functions and the underlying programming elements. The choice of passing mechanism is determined by the presence of the ByVal or ByRef keyword in the function declaration for each parameter.

By utilizing the ByVal keyword, arguments are passed by value, ensuring that modifications within the function do not affect the original calling code. Conversely, the ByRef keyword facilitates passing arguments by reference, allowing the function to modify the original data within the calling code. This careful control over argument passing empowers developers to manage data integrity and effectively utilize functions to suit specific programming requirements.


ByVal in Visual Basic .NET signifies that a copy of the provided value is sent to the function. When dealing with value types like Integer, Single, etc., this results in a shallow copy of the value, which is generally efficient. However, for larger types, this can be less efficient due to the overhead of copying data. On the other hand, when dealing with reference types like String or class instances, a copy of the reference is passed, rather than the actual data.

Because a copy of the value or reference is passed, any modifications made to the parameter within the function will not be visible to the calling function. This behavior ensures that changes to the parameter do not affect the original variable at the call site. In essence, passing by value is akin to creating another variable within the method, and any modifications to it are isolated within the method's scope, leaving the original variable unchanged at the calling function.

It is essential to consider the implications of ByVal when working with large data structures to avoid unnecessary overhead, and to be mindful of the distinction between value types and reference types to understand how the parameters are being passed to functions.


When a parameter is passed by reference (ByRef), a reference to the original value or object is sent to the function. This means that any operations performed on the parameter within the function directly affect the original value in the calling code. Changes made to the parameter using the "=" operator or other modifications will be immediately visible in the calling function because both the function and the calling code share the same reference to the data.

Using ByRef is particularly useful when you need a function to modify the original data and have those modifications reflected in the calling code. This behavior allows for two-way communication between the function and the calling code, making it possible to perform transformations on the data without the need to return the modified value explicitly.


In Visual Basic, the default mechanism for passing arguments to functions is "by value." To enhance code readability and promote good programming practices, it is advisable to explicitly use the ByVal keyword when declaring parameters. Employing the ByVal keyword clarifies that arguments are being passed by value, thereby making the code more comprehensible and reducing ambiguity. It is considered a best practice to include either the ByVal or ByRef keyword for each declared parameter, as it not only ensures clarity but also facilitates better code maintenance and understanding for developers working on the project.