Overloading the vb.net & operator in a c# class

Question

I have an incredibly unique problem here. Our business application has been built using c# and vb.net. We have been trying to approach a standard and trim the fat for some of our core, already duplicated, objects. We are getting really close, but when trying to consolidate a duplicate object into c# our vb.net code now starts throwing the error "Operator '&' is not defined for type 'CSType' and 'String', when I try to do vb.net string concatenation using the ampersand(&). The funny thing is that if I use the '&' in c# with CSType (after properly overloading it) i get the string concatenation I expect.

Here are my basic overloads on CSType:

public static string operator &(CSType c1, string s2)
{
    return c1.ToString() + s2;
}
public static string operator &(string s1, CSType c2) 
{
    return s1 + c2.ToString();
}

When I run the '&' operator in c# with a CSType and a string, I get the expected results, when I attempt to execute that in vb.net the code will not compile giving me an error that:

"Operator '&' is not defined for types 'CSType' and 'String'"

CSType also implicitly converts to most data types, so I was thinking that there may have been some issue with the '&' assuming that it was a bitwise operator, but I would guess that would fails by giving me messed up execution, not a compile error.

Anyway, I'm of half a mind to place this class in c++ where I know I can get what I need out of it, but isn't 2 languages enough already.

(I think the implication here is that you'll need to provide a cast operator overload for string and use CType in VB.NET.) — Markus
– Markus, Commented Jun 12, 2014 at 0:28
Don't use operator overloading for business applications. :) — Victor Zakharov
– Victor Zakharov, Commented Jun 12, 2014 at 0:52

sloth · Accepted Answer · 2014-06-12 09:01:30Z

5

The & operator in C# is the bitwise AND operator. So when you overload it like

public static string operator &(CSType c1, string s2)
{
    return c1.ToString() + s2;
}
public static string operator &(string s1, CSType c2) 
{
    return s1 + c2.ToString();
}

you can use it in VB.Net with the And operator:

Dim a = New CSType("Foo")
Dim b = "Bar"
Dim c = a And b

However, to overload VB.Net's & operator outside of VB.Net (e.g. C#), you have to create a method named op_Concatenate and use the SpecialName attribute:

[SpecialName]
public static string op_Concatenate(CSType c1, string s2)
{
    return c1.ToString() + s2;
}

[SpecialName]
public static string op_Concatenate(string s1, CSType c2)
{
    return s1 + c2.ToString();
}

Then the following code will work:

Dim a = New CSType("Foo")
Dim b = "Bar"
Dim c = a & b

answered Jun 12, 2014 at 9:01

sloth

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1 Comment

zeedub Over a year ago

Thank you, this was incredibly helpful!

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