Adding support for constrained open generics

[jbogard]

(again)

See #471 for details. Figured I'd give this another shot.

The general scenario is:

Suppose I have some interface, IRepository<T>. This interface allows me to save an entity to a database, perhaps wrapping EFCore DbContext. As part of saving, I want to validate so I have IValidator<T>.

The implementation DbContextRepository<T> uses an enumerable of IValidator<T> to validate:

class DbContextRepository<T> {
    public DbContextRepository(
        DbContext db, 
        IEnumerable<IValidator<T>> validators) {
        // etc
    }
}

I want to be able to support:

class IFooValidator<T> : IValidator<T> where T : IFoo { }

instead of

class IFooValidator : IValidator<IFoo> {}

For the reasons in #471.

In case anything has changed, just wanted to throw this out there. I modified the approach to do what Autofac does, which is actually check the constraints if they exist (instead of the previous try-catch-swallow approach).

[muratg]

@davidfowl could you either merge or close this? @natemcmaster is going to move this to the mondo repo and moving PRs are tricky. Thanks.

[jbogard]

I vote the first ;)

On Wed, Oct 17, 2018 at 5:10 PM Murat Girgin notifications@github.com wrote:

@davidfowl https://github.com/davidfowl could you either merge or close this? @natemcmaster https://github.com/natemcmaster is going to move this to the mondo repo and moving PRs are tricky. Thanks.

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[pakrym]

We would like to get this feature in for 3.0 but in a bit different shape (I managed to convince @davidfowl to catch first chance exceptions). It means, unfortunately, this PR would have to be closed and reopened against new repo.

[jbogard]

I’ll reopen on the new repo when it shows up then.

On Wed, Oct 17, 2018 at 5:44 PM Pavel Krymets notifications@github.com wrote:

We would like to get this feature in for 3.0 but in a bit different shape (I managed to convince @davidfowl https://github.com/davidfowl to catch first chance exceptions). It means, unfortunately, this PR would have to be closed and reopened against new repo.

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[muratg]

Thanks @jbogard!

[davidfowl]

first chance exceptions are the 👿. We should do what we can in ns2.0 and ask for new APIs in corefx to make it possible to avoid throwing.

[jbogard]

@davidfowl I agree but this is what every container developer has had to deal with. May be easier now to expose the APIs now.