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examples: Add stricter impl trait bounds #1518

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Sep 30, 2024
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examples: Add stricter impl trait bounds #1518

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16 changes: 14 additions & 2 deletions examples/virtual_methods/cat.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -96,7 +96,19 @@ impl Default for Cat {
///
/// By convention we still create an empty `CatImpl` trait, this allows us to add
/// 'protected' cat methods only available to be called by other Cats later.
pub trait CatImpl: PetImpl {}
pub trait CatImpl: PetImpl
where
<Self as ObjectSubclass>::Type: IsA<glib::Object>,
<Self as ObjectSubclass>::Type: IsA<Pet>,
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This one is not inferred by requiring PetImpl, and PetImpl requiring IsA<Pet>?

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It is required, not inferred. Therefore it is showing an error if not specified.

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error[E0277]: the trait bound `<Self as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>` is not satisfied
   --> examples/virtual_methods/cat.rs:99:20
    |
99  | pub trait CatImpl: PetImpl
    |                    ^^^^^^^ the trait `glib::object::IsA<pet::Pet>` is not implemented for `<Self as glib::subclass::types::ObjectSubclass>::Type`
    |
note: required by a bound in `pet::PetImpl`
   --> examples/virtual_methods/pet.rs:130:37
    |
128 | pub trait PetImpl: ObjectImpl
    |           ------- required by a bound in this trait
129 | where
130 |     <Self as ObjectSubclass>::Type: IsA<Pet>,
    |                                     ^^^^^^^^ required by this bound in `PetImpl`
help: consider further restricting the associated type
    |
101 |     <Self as ObjectSubclass>::Type: IsA<Cat>, <Self as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>
    |                                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

error[E0277]: the trait bound `<Obj as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>` is not satisfied
   --> examples/virtual_methods/cat.rs:106:28
    |
106 | unsafe impl<Obj: CatImpl + PetImpl> IsSubclassable<Obj> for Cat where
    |                            ^^^^^^^ the trait `glib::object::IsA<pet::Pet>` is not implemented for `<Obj as glib::subclass::types::ObjectSubclass>::Type`
    |
note: required by a bound in `pet::PetImpl`
   --> examples/virtual_methods/pet.rs:130:37
    |
128 | pub trait PetImpl: ObjectImpl
    |           ------- required by a bound in this trait
129 | where
130 |     <Self as ObjectSubclass>::Type: IsA<Pet>,
    |                                     ^^^^^^^^ required by this bound in `PetImpl`
help: consider further restricting the associated type
    |
107 |     <Obj as ObjectSubclass>::Type: IsA<Cat>, <Obj as glib::subclass::types::ObjectSubclass>::Type: glib::object::IsA<pet::Pet>
    |                                            +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

For more information about this error, try `rustc --explain E0277`.
error: could not compile `gtk-rs-examples` (bin "virtual_methods") due to 2 previous errors

<Self as ObjectSubclass>::Type: IsA<Cat>,
{
}

/// To make this class subclassable we need to implement IsSubclassable
unsafe impl<Obj: CatImpl + PetImpl> IsSubclassable<Obj> for Cat {}
unsafe impl<Obj: CatImpl + PetImpl> IsSubclassable<Obj> for Cat
where
<Obj as ObjectSubclass>::Type: IsA<glib::Object>,
<Obj as ObjectSubclass>::Type: IsA<Pet>,
<Obj as ObjectSubclass>::Type: IsA<Cat>,
{
}
25 changes: 21 additions & 4 deletions examples/virtual_methods/pet.rs
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Expand Up @@ -125,7 +125,11 @@ pub trait PetExt: IsA<Pet> {
impl<T: IsA<Pet>> PetExt for T {}

/// The `PetImpl` trait contains overridable virtual function definitions for [`Pet`] objects.
pub trait PetImpl: ObjectImpl {
pub trait PetImpl: ObjectImpl
where
<Self as ObjectSubclass>::Type: IsA<glib::Object>,
<Self as ObjectSubclass>::Type: IsA<Pet>,
{
/// Default implementation of a virtual method.
///
/// This always calls into the implementation of the parent class so that if
Expand All @@ -148,7 +152,11 @@ pub trait PetImpl: ObjectImpl {
/// The `PetImplExt` trait contains non-overridable methods for subclasses to use.
///
/// These are supposed to be called only from inside implementations of `Pet` subclasses.
pub trait PetImplExt: PetImpl {
pub trait PetImplExt: PetImpl
where
<Self as ObjectSubclass>::Type: IsA<glib::Object>,
<Self as ObjectSubclass>::Type: IsA<Pet>,
{
/// Chains up to the parent implementation of [`PetImpl::pet`]
fn parent_pet(&self) -> bool {
let data = Self::type_data();
Expand All @@ -169,10 +177,19 @@ pub trait PetImplExt: PetImpl {
}

/// The `PetImplExt` trait is implemented for all subclasses that have [`Pet`] in the class hierarchy
impl<T: PetImpl> PetImplExt for T {}
impl<T: PetImpl> PetImplExt for T
where
<Self as ObjectSubclass>::Type: IsA<glib::Object>,
<Self as ObjectSubclass>::Type: IsA<Pet>,
{
}

/// To make this class subclassable we need to implement IsSubclassable
unsafe impl<Obj: PetImpl> IsSubclassable<Obj> for Pet {
unsafe impl<Obj: PetImpl> IsSubclassable<Obj> for Pet
where
<Obj as ObjectSubclass>::Type: IsA<glib::Object>,
<Obj as ObjectSubclass>::Type: IsA<Pet>,
{
/// Override the virtual method function pointers in subclasses to call directly into the
/// `PetImpl` of the subclass.
///
Expand Down
25 changes: 21 additions & 4 deletions examples/virtual_methods/purrable.rs
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Expand Up @@ -82,7 +82,11 @@ pub trait PurrableExt: IsA<Purrable> {
impl<T: IsA<Purrable>> PurrableExt for T {}

/// The `PurrableImpl` trait contains virtual function definitions for [`Purrable`] objects.
pub trait PurrableImpl: ObjectImpl {
pub trait PurrableImpl: ObjectImpl
where
<Self as ObjectSubclass>::Type: IsA<glib::Object>,
<Self as ObjectSubclass>::Type: IsA<Purrable>,
{
/// Return the current purring status.
///
/// The default implementation chains up to the parent implementation,
Expand All @@ -96,7 +100,11 @@ pub trait PurrableImpl: ObjectImpl {
/// The `PurrableImplExt` trait contains non-overridable methods for subclasses to use.
///
/// These are supposed to be called only from inside implementations of `Pet` subclasses.
pub trait PurrableImplExt: PurrableImpl {
pub trait PurrableImplExt: PurrableImpl
where
<Self as ObjectSubclass>::Type: IsA<glib::Object>,
<Self as ObjectSubclass>::Type: IsA<Purrable>,
{
/// Chains up to the parent implementation of [`PurrableExt::is_purring`]
fn parent_is_purring(&self) -> bool {
let data = Self::type_data();
Expand All @@ -109,10 +117,19 @@ pub trait PurrableImplExt: PurrableImpl {
}

/// The `PurrableImplExt` trait is implemented for all classes that implement [`Purrable`].
impl<T: PurrableImpl> PurrableImplExt for T {}
impl<T: PurrableImpl> PurrableImplExt for T
where
<Self as ObjectSubclass>::Type: IsA<glib::Object>,
<Self as ObjectSubclass>::Type: IsA<Purrable>,
{
}

/// To make this interface implementable we need to implement [`IsImplementable`]
unsafe impl<Obj: PurrableImpl> IsImplementable<Obj> for Purrable {
unsafe impl<Obj: PurrableImpl> IsImplementable<Obj> for Purrable
where
<Obj as ObjectSubclass>::Type: IsA<glib::Object>,
<Obj as ObjectSubclass>::Type: IsA<Purrable>,
{
fn interface_init(iface: &mut glib::Interface<Self>) {
let klass = iface.as_mut();

Expand Down
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