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Consider moving objc2_foundation into the objc2 crate #39
Description
There's a lot of places in objc2_foundation that would benefit from being able to implement From for specific Ids:
NSArray::from_vecNSArray::into_vecNSData::from_vecNSDictionary::from_keys_and_objectsNSString::from_str- And so on...
Same goes for traits like Default.
But unfortunately, we can't create these implementations because Id is defined in another crate, see RFC 2451. I tried creating a helper trait FromId for this purpose, but that doesn't work either:
pub trait FromId<T, O: Ownership> {
fn from_id(obj: Id<T, O>) -> Self;
}
impl<T, O: Ownership, X: FromId<T, O>> From<Id<T, O>> for X {
fn from(obj: Id<T, O>) -> Self {
Self::from_id(obj)
}
}
// Errors with:
// note: conflicting implementation in crate `core`:
// - impl<T> From<T> for T;
// note: downstream crates may implement trait `FromId<_, _>` for type `Id<_, _>`Though doing it for Default would:
// In objc2:
pub trait IdDefault: Sized {
type Ownership: Ownership;
fn id_default() -> Id<Self, Self::Ownership>;
}
impl<T: IdDefault> Default for Id<T, T::Ownership> {
fn default() -> Self {
T::id_default()
}
}
// In objc2_foundation:
impl IdDefault for NSString {
type Ownership = <NSString as INSObject>::Ownership;
fn id_default() -> Id<Self, Self::Ownership> {
<NSString as INSObject>::new()
}
}So possible solutions:
- Move
objc2_foundationtoobjc2::foundation(under a feature flag) - Move
Idtoobjc2_foundation?
Activity
madsmtm commentedon Oct 6, 2021
Might also be relevant to move most of the implementation of
objc2_exceptionintoobjc2.It currently uses an
Exceptiontype that doesn't implementEncodeandMessage, and it links manually tolibobjc. Of course, these could be alleviated by introducingobjc2_encodeandobjc2_sysas dependencies of it.But it also returns
*mut Exceptioninstead of the correctId<Exception, Shared>, and the only way to fix that is by moving the implementation toobjc2.madsmtm commentedon Oct 15, 2021
I think we may move the
objc2_exceptionimplementation at some point, but theobjc2_foundationseparation should stay; it is fundamentally separate from theobjc2crate, and having these limitations in our own crate encourages us to create helper traits (likeDefaultIdand such, see #41) that can be used by all downstream crates.madsmtm commentedon Oct 15, 2021
I asked on the forum whether this is possible, we'll see if someone comes up with something; otherwise people will just have to import
FromId/IntoIdand usefrom_id/into_idmanuallymadsmtm commentedon Oct 31, 2021
I'm not gonna move
objc2_foundation, so I'll close this issue. Whether to use the approach in #48 or #50 can be determined in the PRs themselves.