Enum ReturnHandling 

pub enum ReturnHandling {
    Unit,
    RawSexp,
    ExternalPtr,
    SelfHandle,
    SelfHandleResult,
    SelfHandleOption,
    IntoR,
    OptionUnit,
    OptionSexp,
    OptionIntoR,
    OptionClassPayload,
    OptionExternalPtr,
    ResultUnit,
    ResultSexp,
    ResultIntoR,
    ResultNullOnErr,
    ResultExternalPtr,
    AsListOf,
    AsExternalPtrOf,
    AsNativeOf,
}

Strategy for converting a Rust return value into an R SEXP.

Determined automatically by detect_return_handling from the function’s return type, or set explicitly via CWrapperContextBuilder::return_handling. Each variant handles a different return type pattern, controlling how the C wrapper converts the Rust value back to R and how errors/None values are surfaced.

Variants

Unit

Returns unit type () – emits R_NilValue.

RawSexp

Returns raw SEXP – passes the value through unchanged (no conversion).

ExternalPtr

Returns Self – wraps the value in an ExternalPtr via ExternalPtr::new.

SelfHandle

Returns &Self / &mut Self (an in-place builder) – evaluates the call for its side effect (the mutation already happened through &mut self), discards the returned borrow, and returns the same self_sexp handle unchanged. This gives R in-place value semantics with no clone: the R object the user piped in is returned verbatim, wrapping the now-mutated Rust value. Only valid for instance methods (requires self_sexp).

SelfHandleResult

Fallible in-place step whose call expression yields Result<(), E> (&mut self -> Result<&mut Self, E>, or self -> Result<Self, E> after the write-back closure): raise on Err, return the same self_sexp handle on Ok (#1432, #1433).

SelfHandleOption

Option sibling of SelfHandleResult: the call yields Option<()>; NULL on None, as every Option return gives, and the same handle on Some.

IntoR

Returns an arbitrary type T: IntoR – converts via IntoR::into_sexp.

OptionUnit

Returns Option<()> – raises an error on None, otherwise emits R_NilValue.

OptionSexp

Returns Option<SEXP> – raises an error on None, otherwise passes through.

OptionIntoR

Returns Option<T> – calls IntoR::into_sexp on the whole Option, so None becomes whatever IntoR for Option<T> gives: NULL for containers, references and pointers, a typed NA for scalars. This is the one rule for an Option<T> return from a standalone function, an inherent method and a trait method (#1415, #2088); detect_return_handling picks it for every Option<T> but the shapes below.

OptionClassPayload

Returns Option<T> under an explicit class wrap (Option<WrapAs*<T>> or wrap = "..."): Some converts the class payload through T: IntoR, None is NULL, as IntoR for Option<T> would give if it could exist (the orphan rule refuses it in the class’s crate). The R wrapper’s class constructor lets NULL through.

OptionExternalPtr

Returns Option<Self> – a lookup-shaped fallible constructor (e.g. try_find). A method-only shape: Some(Self) is wrapped in an ExternalPtr via ExternalPtr::new (same as ExternalPtr), since Self generally has no IntoR, and the Option<ExternalPtr<Self>> converts as any Option does: None is NULL. The R-side wrapper treats a non-NULL value exactly like a bare Self return (wrapped class object via ReturnStrategy::for_method — see ParsedMethod::returns_option_self).

ResultUnit

Returns Result<(), E> – raises an error on Err, otherwise emits R_NilValue.

ResultSexp

Returns Result<SEXP, E> – raises an error on Err, otherwise passes through.

ResultIntoR

Returns Result<T, E> – raises an error on Err, otherwise converts via IntoR::into_sexp.

ResultNullOnErr

Returns Result<T, ()> – maps Err(()) to Err(NullOnErr) then converts via IntoR. None/Err maps to R NULL (unit error is a deliberate sentinel, not a Rust failure).

ResultExternalPtr

Returns Result<Self, E> – a fallible constructor-shaped method (e.g. from_r, try_new). Raises an error on Err (same as ResultIntoR), but wraps Ok(Self) in an ExternalPtr via ExternalPtr::new (same as ExternalPtr) instead of routing it through IntoR (which Self generally does not implement). The R-side wrapper mirrors this: a successful return is treated exactly like a bare Self return (wrapped class object via ReturnStrategy::for_method — see ParsedMethod::returns_result_self).

AsListOf

Returns T where T: IntoList – wraps in AsList(result) then calls IntoR::into_sexp.

Produced when #[miniextendr(prefer = "list")] is used on a function returning T: IntoList. Distinct from returning AsList<T> explicitly only in that the wrapping is generated by the macro rather than written by the user.

AsExternalPtrOf

Returns T where T: IntoExternalPtr – wraps in AsExternalPtr(result) then calls IntoR::into_sexp.

Produced when #[miniextendr(prefer = "externalptr")] is used on a function returning T: IntoExternalPtr. Distinct from the existing ExternalPtr variant (which boxes Self via ExternalPtr::new): this variant calls IntoExternalPtr::into_external_ptr() on T.

AsNativeOf

Returns T where T: RNativeType – wraps in AsRNative(result) then calls IntoR::into_sexp.

Produced when #[miniextendr(prefer = "native")] is used on a function returning T: RNativeType.

Trait Implementations

impl Clone for ReturnHandling

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ReturnHandling

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

Formats the value using the given formatter.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 1 byte

Size for each variant:

• Unit: 0 bytes
• RawSexp: 0 bytes
• ExternalPtr: 0 bytes
• SelfHandle: 0 bytes
• SelfHandleResult: 0 bytes
• SelfHandleOption: 0 bytes
• IntoR: 0 bytes
• OptionUnit: 0 bytes
• OptionSexp: 0 bytes
• OptionIntoR: 0 bytes
• OptionClassPayload: 0 bytes
• OptionExternalPtr: 0 bytes
• ResultUnit: 0 bytes
• ResultSexp: 0 bytes
• ResultIntoR: 0 bytes
• ResultNullOnErr: 0 bytes
• ResultExternalPtr: 0 bytes
• AsListOf: 0 bytes
• AsExternalPtrOf: 0 bytes
• AsNativeOf: 0 bytes