重新实现Enum.HasFlag以在Mono 2.6中使用

Question

I'm trying to convert Jint for use in Mono 2.6. Unfortunately Mono 2.6 doesn't have Enum.HasFlag and that's something they use in Jint. I should also add that I'm quite new to C#.

According to the MSDN page ( http://msdn.microsoft.com/en-us/library/system.enum.hasflag(v=vs.110).aspx ) the implementation should be

thisInstance And flag = flag

but this doesn't seem to make a lot of sense. If these are all bitwise operations shouldn't it be more like this?

thisInstance & flag == flag

So, the line I'm trying to modify is

Writable = !fieldInfo.Attributes.HasFlag(FieldAttributes.InitOnly);

I've stuck this in

var thisInstance = fieldInfo.Attributes;
var thisFlag = FieldAttributes.InitOnly;
var hasFlag1 = thisInstance & thisFlag == thisFlag;
var hasFlag2 = thisInstance And thisFlag = thisFlag;
Writable1 = !hasFlag1;
Writable2 = !hasFlag2;

and understandably the compiler doesn't like either of these. For hasFlag1 I get

Operator '&' cannot be applied to operands of type 'System.Reflection.FieldAttributes' and 'bool'

And for hasFlag2:

Unexpected symbol 'And'

Just want to know if anyone knows how this is meant to be done.

Thanks!

Answer 1

It seems based on the error of the compiler that == takes precedence over &. Therefore your line is evaluated like this: var hasFlag1 = thisInstance & (thisFlag == thisFlag);

What you want is this:

var hasFlag1 = (thisInstance & thisFlag) == thisFlag;

So if you add the parentheses, the compiler error should go away.

Most probably And is the VB equivalent of &