Question

I’m trying create new object from a module class in VBA, and I have a small diffcult. Two line of assigning code, look like the same, but result is different.

I got a error message:

After that, I switch to use (1) instead of (2), error was fixed.

But I dont understand; Why do they have this difference?

Answer 1

If you do not use Dim to declare the specific type of a variable you may subsequently change the variable to another type, for example after;

set aosh = new AOSHRatioQuery

You could mutate the variable to a string;

aosh = "A pint of milk"

As the sendAsyncRequest method expects a AOSHRatioQuery as its 2nd argument & the VBA compiler knows that it cannot guarantee that the aosh variable will actually contain an instance of that type, type safety is violated & the Type Mismatch error is raised to prevent sendAsyncRequest from receiving garbage it cannot interpret.

Explicitly typing with Dim aosh as new AOSHRatioQuery tells the compiler that aosh is guaranteed to always be AOSHRatioQuery instance or Nothing (attempting to assign it to another type will raise an error) so it can be passed safely.