Module objc2::mutability

Marker types for class mutability.

Every class must indicate which kind of mutability its instances use:

• Is the instance mutable or immutable?
• Does it use interior mutability (mutable behind &self, like UnsafeCell)?
• Does it access global statics in such a way that the type is only safe to use from the main thread?

The answer to these facts influence the final capabilities the type has, as encoded in the traits in this module.

Concretely, you set ClassType::Mutability to one of the types in this module to indicate the properties of class you’re dealing with (can be done inside extern_class! and declare_class!).

Note that precious little of Objective-C follows Rust’s usual shared xor unique ownership model, most often objects assume interior mutability, so a safe default is often InteriorMutable, or of you’re working with GUI code, MainThreadOnly.

SemVer

It is considered a major change to change the ClassType::Mutability of an object, though it can be done as a minor change in some cases to fix a bug.

Structs

• Immutable
  Marker type for immutable classes.
• ImmutableWithMutableSubclass
  Marker type for immutable classes that have a mutable counterpart.
• InteriorMutable
  Marker type for classes that use interior mutability.
• MainThreadOnly
  Marker type for classes that are only safe to use from the main thread.
• Mutable
  Marker type for mutable classes.
• MutableWithImmutableSuperclass
  Marker type for mutable classes that have a immutable counterpart.
• Root
  Marker type for root classes.

Traits

• CounterpartOrSelf
  Retrieve the immutable/mutable counterpart class, and fall back to Self if not applicable.
• HasStableHash
  Marker trait for classes whose hash and isEqual: methods are stable.
• IsAllocableAnyThread
  Marker trait for classes that can be allocated from any thread.
• IsAllowedMutable
  Marker trait for classes that may feasibly be used behind a mutable reference.
• IsIdCloneable
  Marker trait for classes where Retained::clone / Id::clone is safe.
• IsMainThreadOnly
  Marker trait for classes that are only available on the main thread.
• IsMutable
  Marker trait for classes that are only mutable through &mut.
• IsRetainable
  Marker trait for classes where the retain selector is always safe.
• Mutability
  Marker trait for the different types of mutability a class can have.