Strange (possibly wrong?) C# compiler behavior with method overloading and enums

Question

today I discovered a very strange behavior with C# function overloading. The problem occurs when I have a method with 2 overloads, one accepting Object and the other accepti

Answer 1

It may be that you're not aware that there's an implicit conversion from a constant¹ of 0 to any enum:

Bar x = 0; // Implicit conversion

Now, the conversion from 0 to Bar is more specific than the conversion from 0 to object, which is why the Foo(Bar) overload is used.

Does that clear everything up?

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¹ There's actually a bug in the Microsoft C# compiler which lets it be any zero constant, not just an integer:

const decimal DecimalZero = 0.0m;

...
Bar x = DecimalZero;

It's unlikely that this will ever be fixed, as it could break existing working code. I believe Eric Lippert has a two blog posts which go into much more detail.

The C# specification section 6.1.3 (C# 4 spec) has this to say about it:

An implicit enumeration conversion permits the decimal-integer-literal 0 to be converted to any enum-type and to any nullable-type whose underlying type is an enum-type. In the latter case the conversion is evaluated by converting to the underlying enum-type and wrapping the result (§4.1.10).

That actually suggests that the bug isn't just in allowing the wrong type, but allowing any constant 0 value to be converted rather than only the literal value 0.

EDIT: It looks like the "constant" part was partially introduced in the C# 3 compiler. Previously it was some constant values, now it looks like it's all of them.