Generics: how to have a constraint on an attribute?

[=?Utf-8?B?TWF0dGVvIENhc2F0aQ==?=]

Hi,
I would like to set a constraint (where keyword) on a type in a generic
class, based on the [Serializable] attribute to accept as "T" type each class
marked as serializable.
Is it possible? If yes, how to do? Else... why not??? :-)
Thanks

[Marc Gravell]

Is it possible?
Not at compile time via a constraint, no.

At runtime, you could check via reflection, but you don't get many
benefits doing this.

why not???

Remember that constraints are compile-time; how many permutations /
combinations should it support? what are the common use-cases? what
level of complexity? Personally I find that the existing limits do
what I need.
A more common question is "can I tell it to demand a constructor
matching (int, string)" etc, but again this isn't supported - just
parameterless.

Marc

[Jon Skeet [C# MVP]]

On Nov 16, 11:48 am, "Marc Gravell" <[e-mail]:

<snip>

A more common question is "can I tell it to demand a constructor
matching (int, string)" etc, but again this isn't supported - just
parameterless.

The two I'd like supported are "T derives from System.Enum" and "T
derives from System.Delegate" - but both of these are specifically
*excluded* from the normal derivation constraints, which is a bit of a
pain :(

Jon

[=?Utf-8?B?TWF0dGVvIENhc2F0aQ==?=]

"Marc Gravell" wrote:

Not at compile time via a constraint, no.

Ok :-(

At runtime, you could check via reflection, but you don't get many
benefits doing this.

Yeah, but this is not a solution: I will have compile time errors also
without the check on IsSerializable :-)

Remember that constraints are compile-time; how many permutations /
combinations should it support? what are the common use-cases? what
level of complexity? Personally I find that the existing limits do
what I need.

I agree!

Thank your for your reply.
Have a nice day.

[=?Utf-8?B?TWF0dGVvIENhc2F0aQ==?=]

[...] both of these are specifically

*excluded* from the normal derivation constraints, which is a bit of a
pain :(

Current supported constraints are too poor to be useful :-(
We can only hope to have an extension of "where" keywords in one of the the
next releases.

Thanks for your answer.
Bye

[Jon Skeet [C# MVP]]

Matteo Casati <Ma**********@discussions.microsoft.comwrote:

[...] both of these are specifically
*excluded* from the normal derivation constraints, which is a bit of a
pain :(

Current supported constraints are too poor to be useful :-(

I wouldn't say that. They're not as useful as they *might* be, but
they're still useful.

We can only hope to have an extension of "where" keywords in one of the the
next releases.

Unfortunately I suspect that would require CLR support, which is
obviously more significant than just library or language support :(

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