VBA This is confusing. Why not just always use parentheses?


Example

Parentheses are used to enclose the arguments of function calls. Using them for procedure calls can cause unexpected problems.

Because they can introduce bugs, both at run-time by passing a possibly unintended value to the procedure, and at compile-time by simply being invalid syntax.

Run-time

Redundant parentheses can introduce bugs. Given a procedure that takes an object reference as a parameter...

Sub DoSomething(ByRef target As Range)
End Sub

...and called with parentheses:

DoSomething (Application.ActiveCell) 'raises an error at runtime

This will raise an "Object Required" runtime error #424. Other errors are possible in other circumstances: here the Application.ActiveCell Range object reference is being evaluated and passed by value regardless of the procedure's signature specifying that target would be passed ByRef. The actual value passed ByVal to DoSomething in the above snippet, is Application.ActiveCell.Value.

Parentheses force VBA to evaluate the value of the bracketed expression, and pass the result ByVal to the called procedure. When the type of the evaluated result mismatches the procedure's expected type and cannot be implicitly converted, a runtime error is raised.

Compile-time

This code will fail to compile:

MsgBox ("Invalid Code!", vbCritical)

Because the expression ("Invalid Code!", vbCritical) cannot be evaluated to a value.

This would compile and work:

MsgBox ("Invalid Code!"), (vbCritical)

But would definitely look silly. Avoid redundant parentheses.