Question

I don’t know how to explain my question, please accept it in example form:

I wrote a library in C# language which has a method as below:

public object GetValueAt(int idx) {
    return arr[idx];
}

Then I use it in VB.Net, ofcourse there’s a diffirent in index based between C# and VB.Net. So if I call that method with idx = 6, how does CLR know object which I try to access (it having idx = 5 on C#)?

That’s just my example, and what about existed library in .Net?

Answer 1

If you call that method from VB with idx = 6 it will return arr[6] treating arr as 0-based (i.e. the seventh element), because the code is written in C#. No automatic rebasing is applied, because you’re just calling a method from VB.

I thought the VB compiler automatically adjusts array indexes when the array indexing expression itself is in VB, but that’s not the case here – it’s just a method call. EDIT: It looks like that doesn’t happen anyway, at least not always. The compiler makes allowances when creating arrays, but not indexing into them, apparently…

EDIT: That chimes in with the MSDN "Arrays In Visual Basic" page which shows an example and explains:

The array students in the preceding example contains 7 elements. The indexes of the elements range from 0 through 6.

And from this blog post:

As many long-time web developers may know, Visual Basic and VB Script used to have 1-based arrays for many years while just about every other language I used — C, C++, JScript, JavaScript — had 0-based arrays. I didn’t particularly have any strong preference for one over the other, but it was tricky to adjust your mind when switching from one to the other.

Then when .Net was released, Visual Basic changed to using 0-based arrays.