Enums and IEquatable<T>

[Marc Gravell]

This one stumped me while refactoring some code to use generics...

Suppose I declare an enum MyEnum {...}

Is there a good reason why MyEnum doesn't implement IEquatable<MyEn um> ?

Of course, I can cast a MyEnum instance down to the int / short whatever
(since int implements IEquatable<int> ), but I don't like doing that, as it
feels a bit messy, and I am then propegating the things that know what the
base represenation is...

Am I missing something? Is this just an oversight?
(For ref, I am using IEquatable<T> to avoid having to use == since operators
cannot be expressed in the delegate declaration).

Marc

[Barry Kelly]

"Marc Gravell" <ma**********@g mail.com> wrote:

(For ref, I am using IEquatable<T> to avoid having to use == since operators
cannot be expressed in the delegate declaration).

Do you mean as a generic type parameter constraint? Consider passing an
argument of type IEqualityCompar er<T> to your constructor if you need to
compare items. You can default it to EqualityCompare r<T>.Default. That
will query for IEquatable<T> and other interfaces to do all the real
work, falling back to object.Equals() if necessary.

-- Barry

--
http://barrkel.blogspot.com/

[Marc Gravell]

A useful tip, thankyou. A shame that it will involve a bit of hacking to get
it to fit my intended usage... oh well...

I still can't help but think that enums should implement this, though ;-p

Marc

[Jay B. Harlow [MVP - Outlook]]

Marc,
| Is there a good reason why MyEnum doesn't implement IEquatable<MyEn um> ?
I don't know, I thought they should...
In addition to other comments, consider using EqualityCompare r(Of T) within
your generic class/method. Something like:

using System.Collecti ons.Generic;

static T Something<T>(T value1, T value2)
{
if (EqualityCompar er<T>.Default.E quals(value1, value2))
return value1;
else
return value2;
}
--
Hope this helps
Jay B. Harlow [MVP - Outlook]
..NET Application Architect, Enthusiast, & Evangelist
T.S. Bradley - http://www.tsbradley.net
"Marc Gravell" <ma**********@g mail.com> wrote in message
news:el******** ********@TK2MSF TNGP04.phx.gbl. ..
| This one stumped me while refactoring some code to use generics...
|
| Suppose I declare an enum MyEnum {...}
|
| Is there a good reason why MyEnum doesn't implement IEquatable<MyEn um> ?
|
| Of course, I can cast a MyEnum instance down to the int / short whatever
| (since int implements IEquatable<int> ), but I don't like doing that, as it
| feels a bit messy, and I am then propegating the things that know what the
| base represenation is...
|
| Am I missing something? Is this just an oversight?
| (For ref, I am using IEquatable<T> to avoid having to use == since
operators
| cannot be expressed in the delegate declaration).
|
| Marc
|
|

[Barry Kelly]

"Jay B. Harlow [MVP - Outlook]" <Ja************ @tsbradley.net> wrote:

In addition to other comments, consider using EqualityCompare r(Of T) within
your generic class/method. Something like:
using System.Collecti ons.Generic;

static T Something<T>(T value1, T value2)
{
if (EqualityCompar er<T>.Default.E quals(value1, value2))

That's what I said!

-- Barry

--
http://barrkel.blogspot.com/

[Jay B. Harlow [MVP - Outlook]]

Barry,
Pardon me! I read your message that you were suggesting passing a parameter.

I was suggesting to forgo the parameter & simply use
EqualityCompare r<T>.Default inline.

--
Hope this helps
Jay B. Harlow [MVP - Outlook]
..NET Application Architect, Enthusiast, & Evangelist
T.S. Bradley - http://www.tsbradley.net
"Barry Kelly" <ba***********@ gmail.com> wrote in message
news:nq******** *************** *********@4ax.c om...
| "Jay B. Harlow [MVP - Outlook]" <Ja************ @tsbradley.net> wrote:
|
| > In addition to other comments, consider using EqualityCompare r(Of T)
within
| > your generic class/method. Something like:
|
|
| > using System.Collecti ons.Generic;
| >
| > static T Something<T>(T value1, T value2)
| > {
| > if (EqualityCompar er<T>.Default.E quals(value1, value2))
|
| That's what I said!
|
| -- Barry
|
| --
| http://barrkel.blogspot.com/

[Marc Gravell]

This is all fine - and I agree that EqualityCompare r<T>.Default is better
than casting to the base type (int or what-have-you), but (back in
problem-town rather than
solution-ville) am I alone in thinking that an enum MyEnum should implement
IEquatable<MyEn um>?

Marc

[Barry Kelly]

"Marc Gravell" <ma**********@g mail.com> wrote:

This is all fine - and I agree that EqualityCompare r<T>.Default is better
than casting to the base type (int or what-have-you), but (back in
problem-town rather than
solution-ville) am I alone in thinking that an enum MyEnum should implement
IEquatable<MyEn um>?

The only thing I can think of is the cost of instantiation: every time a
generic type is instantiated, either memory usage or executables get
bigger. Could be an issue for compact framework etc.

-- Barry

--
http://barrkel.blogspot.com/

[Marc Gravell]

I guess that makes some sense, especially when you consider how structs and
generics behave; and there's a lot of enums in the framework, so if each of
those declared their own IEquatable<some struct>...

Interesting theory - cheers,

Marc

[Jay B. Harlow [MVP - Outlook]]

Marc,
| am I alone in thinking that an enum MyEnum should implement
| IEquatable<MyEn um>?
No you are not alone, I think they should also!

Personally I find the news Java Enum to be "better" then the .NET enum...

http://java.sun.com/j2se/1.5.0/docs/...age/enums.html

--
Hope this helps
Jay B. Harlow [MVP - Outlook]
..NET Application Architect, Enthusiast, & Evangelist
T.S. Bradley - http://www.tsbradley.net
"Marc Gravell" <ma**********@g mail.com> wrote in message
news:ez******** ******@TK2MSFTN GP05.phx.gbl...
| This is all fine - and I agree that EqualityCompare r<T>.Default is better
| than casting to the base type (int or what-have-you), but (back in
| problem-town rather than
| solution-ville) am I alone in thinking that an enum MyEnum should
implement
| IEquatable<MyEn um>?
|
| Marc
|
|