Enum VTableEntry 

pub enum VTableEntry {
    Direct {
        function_id: u16,
    },
    Closure {
        function_id: u32,
        type_id: u32,
    },
    BoxedReturn {
        thunk_id: u16,
        wrap_targets: SmallVec<[WrapTarget; 2]>,
    },
    SelfArg {
        thunk_id: u16,
        self_arg_positions: SmallVec<[u8; 4]>,
    },
    Generic {
        thunk_id: u16,
        type_param_count: u8,
    },
    Compound {
        thunk_id: u16,
        flags: VTableEntryFlags,
        wrap_targets: SmallVec<[WrapTarget; 2]>,
        self_arg_positions: SmallVec<[u8; 4]>,
        type_param_count: u8,
    },
}

How a single trait method dispatches through dyn T.

Six variants cover the cross-product of (no rewriting / Self-in-return / Self-in-arg / method-generic) per ADR-006 §2.7.24 Q25.C.5. The plain (function_id) and (function_id + type_id) entries preserve the pre-§2.7.24 vtable shapes so existing emit-tier wiring continues to compile.

Thunks vs function ids: variants other than Direct / Closure carry a thunk_id rather than a raw function id. The compiler-side vtable-construction tier generates one thunk per (impl, method) pair whose Erase_T-rewritten signature differs from the underlying impl method; the thunk does the auto-boxing on return / vtable-identity check / TypeInfo dispatch / etc., then tail-calls the impl method.

Variants

Direct

Direct call — no Erase_T rewriting needed (no Self in non-receiver position, no method-generic parameters). Dispatch is a simple function-id call. Preserves the pre-§2.7.24 VTableEntry::FunctionId(u16) shape (renamed function_id field for forward consistency).

Fields

function_id: u16

Closure

Pre-existing closure entry (W7 closure trait impls).

VTable closure entries carry (function_id, type_id); dispatch allocates a fresh OwnedClosureBlock per call via the program’s closure_function_layouts registry so the call convention sees the same raw TypedClosureHeader shape that op_make_closure emits.

Fields

function_id: u32

type_id: u32

BoxedReturn

Self (or Self::A) appears in return position. The thunk wraps the impl’s concrete return value back into a dyn T carrier at each wrap_targets path before returning.

Fields

thunk_id: u16

wrap_targets: SmallVec<[WrapTarget; 2]>

One entry per place the impl’s signature names Self / Self::A inside its (possibly structural) return type. E.g. for fn try_clone(&self) -> Result<Self, Error>, wrap_targets = [WrapTarget { path: [0], wrap_as_trait_id }].

SelfArg

Self appears in argument position. The thunk checks vtable-identity (per §Q25.C.2) between self’s vtable and each Self-typed argument’s vtable before forwarding to the impl method.

Fields

thunk_id: u16

self_arg_positions: SmallVec<[u8; 4]>

Argument indices (0-based, excluding the receiver) at which the impl’s signature names Self directly. Each gets one Arc::ptr_eq check on its vtable before dispatch.

Generic

Method has type parameters (fn method<G: Bound>(&self, g: G)). The thunk consumes type_param_count &TypeInfo parameters alongside the regular arguments per §Q25.C.3 and dispatches on concrete_type_id for each.

Fields

thunk_id: u16

type_param_count: u8

Compound

Combination of BoxedReturn / SelfArg / Generic. The thunk dispatches per flags bit set.

Fields

thunk_id: u16

flags: VTableEntryFlags

wrap_targets: SmallVec<[WrapTarget; 2]>

self_arg_positions: SmallVec<[u8; 4]>

type_param_count: u8

Trait Implementations

impl Clone for VTableEntry

fn clone(&self) -> VTableEntry

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for VTableEntry

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.