Trait VTable

Source

pub unsafe trait VTable: Clone {
    type Bounds: IsBound;
    type Id: PartialEq + Eq;

    // Required methods
    fn descriptor(&self) -> &Descriptor<Self::Id>;
    fn bound_impl(&self) -> &BoundsImpl<Self::Bounds>;
}

Expand description

Virtual method table and type descriptor.

Rust automatically generates vtables for trait objects. However, its not currently possible to access these vtables directly on stable. Instead, this trait provides a unified interface for custom vtables. Custom vtables can be generated thanks to Rust’s ability to static promote constants to give them stable addresses.

A vtable is created from a type Descriptor and a BoundsImpl. A Descriptor describes a type, and includes things like the type’s size and name. The Descriptor::is_type() method can be used to check if a vtable is for a particular type. A BoundsImpl contains the implementations of the virtual methods for the type. Currently, only Drop, Clone, and Debug are included in the virtual methods.

All dungeon_cell types use this trait as the basis for their type erasure.

Use VTableOf or ConstVTableOf to construct a instance of a generic vtable for a type. Additionally, use VTableSubset to reduce the number of traits bound by Self::Bounds.

§Safety

The type described by Self::descriptor() must be the same that Self::bound_impl was created for. This means calling Descriptor::new::<T>() and BoundsImpl::new::<T>() with the same T.
The type Self::Id must be well behaved. This means that when performing equality between two Self::Id if the result is true then the type T that Self::descriptor() describes is the same type. Additionally, Inspect::<Self::Id>::inspect::<T>() must return the Self::Id for the type T following this equality.
The type the vtable describes must implement the traits given by Self::Bounds.