Struct BuiltList 

pub struct BuiltList {
    view: List,
    root: Preserved,
}

An owned, GC-rooted R list: the plain-list finish of NamedListBuilder.

The list analogue of BuiltDataFrame: it holds a Preserved root for as long as it lives (!Send + !Sync), dereferences to the List view for reads, and returns to R through IntoR. set_class and set_attr allocate while the list stays rooted, and return the handle, so a chain is rooted at every link:

let out = columns.into_list().set_class(&["my_result", "list"]);
call_r_helper(out.as_sexp()); // `out` keeps the list alive across the call
out

A List copied out of the handle (*out) is an unrooted view: it stays valid only while the handle lives.

Fields

view: List

root: Preserved

Roots view’s list for as long as the handle lives.

Implementations

impl BuiltList

unsafe fn from_root(root: Preserved) -> Self

Take over an existing root of a list.

Safety

root holds a VECSXP.

pub fn set_class(self, classes: &[&str]) -> Self

Set the class attribute.

pub fn set_attr(self, name: &str, value: impl IntoR) -> Self

Set the attribute name to value.

Methods from Deref<Target = List>

pub fn as_data_frame(&self) -> Result<BuiltDataFrame, DataFrameError>

Promote this named list to a DataFrame.

Errors

Returns DataFrameError if the list has no names or columns differ in length.

pub fn is_list(self) -> bool

Return true if the underlying SEXP is a list (VECSXP) according to R.

Uses SexpExt::is_list (VECSXP check) — not is_pair_list (LISTSXP).

pub fn as_sexp(self) -> SEXP

Get the underlying SEXP.

pub fn len(self) -> isize

Length of the list (number of elements).

pub fn is_empty(self) -> bool

Returns true if the list is empty.

pub fn get(self, idx: isize) -> Option<SEXP>

Get raw SEXP element at 0-based index. Returns None if out of bounds.

pub fn get_index<T>(self, idx: isize) -> Option<T>

where T: TryFromSexp,

Get element at 0-based index and convert to type T.

Returns None if index is out of bounds or conversion fails.

The conversion error is discarded, so T’s TryFromSexp::Error is unconstrained — any element type works, not only those whose error is SexpError. Callers that need the error (e.g. to distinguish “missing” from “wrong type”) should use get and convert directly.

fn text_names(self) -> impl Iterator<Item = (isize, &'static str)>

The names this list can be looked up by: (position, name) for each element whose name is neither NA nor invalid UTF-8, in list order. Empty names are included. Yields nothing when the list has no names attribute.

get_named_sexp, first_duplicate_name, NamedList and the #[derive(TryFromList)] field lookup all walk the names through this, so they agree on which names count.

The &strs point into R’s CHARSXP cache; they stay valid while the list (which roots its names attribute) is reachable.

pub fn get_named_sexp(self, name: &str) -> Option<SEXP>

Get the raw element SEXP associated with name, without conversion.

Returns the element exactly as stored so callers can convert it with any TryFromSexp error type — not only those whose error is SexpError. Returns None when the list has no names attribute or no name matches.

When the name appears more than once, the first element with that name is returned, as R’s x[["name"]] does.

pub fn first_duplicate_name(self) -> Option<String>

The first name that appears more than once in the list, if any.

An R list may repeat a name (list(a = 1, a = 2)), and a List argument accepts such a list, as R does. A function that needs each name to be unique checks for it itself, and words its own error:

use miniextendr_api::{List, miniextendr};

#[miniextendr]
pub fn settings_count(settings: List) -> i32 {
    if let Some(name) = settings.first_duplicate_name() {
        panic!("`settings` has the name {name:?} more than once; each entry needs a unique name");
    }
    settings.len() as i32
}

Only names that can identify an element are compared: NA and empty names are skipped (R lets any number of elements go unnamed), and so are names that are not valid UTF-8. Returns None for a list without a names attribute.

#[doc(hidden)]

pub fn __mx_field_positions<const N: usize>( self, sorted_fields: [&str; N], ) -> Result<[Option<isize>; N], SexpError>

Positions of a derived struct’s fields, for the code #[derive(TryFromList)] generates. Not public API.

sorted_fields holds the struct’s field names in ascending byte order (the derive sorts them); entry k of the result is the position of the first element named sorted_fields[k], or None when no element has that name. One pass over the names, O(n log fields).

A field name that appears more than once is an error (SexpError::DuplicateName): the struct could only keep one of the values. Other repeated names are ignored, as names that are not fields are.

pub fn get_named<T>(self, name: &str) -> Option<T>

where T: TryFromSexp,

Get element by name and convert to type T.

Returns None if name not found or conversion fails.

The conversion error is discarded, so T’s TryFromSexp::Error is unconstrained. Use get_named_sexp and convert directly when you need to inspect the conversion failure.

fn get_attr_opt(self, name: SEXP) -> Option<SEXP>

Get an arbitrary attribute by symbol, returning None for R_NilValue.

pub fn names(self) -> Option<SEXP>

Get the names attribute if present.

pub fn get_class(self) -> Option<SEXP>

Get the class attribute if present.

pub fn get_dim(self) -> Option<SEXP>

Get the dim attribute if present.

pub fn get_dimnames(self) -> Option<SEXP>

Get the dimnames attribute if present.

pub fn get_rownames(self) -> Option<SEXP>

Get row names from the dimnames attribute.

pub fn get_colnames(self) -> Option<SEXP>

Get column names from the dimnames attribute.

pub fn get_levels(self) -> Option<SEXP>

Get the levels attribute if present (for factors).

pub fn get_tsp(self) -> Option<SEXP>

Get the tsp attribute if present (for time series).

pub fn set_names(self, names: SEXP) -> Self

Set the names attribute; returns the same list for chaining.

Equivalent to R’s SET_NAMES(x, n).

pub fn set_class(self, class: SEXP) -> Self

Set the class attribute; returns the same list for chaining.

Equivalent to R’s SET_CLASS(x, n).

pub fn set_dim(self, dim: SEXP) -> Self

Set the dim attribute; returns the same list for chaining.

Equivalent to R’s SET_DIM(x, n).

pub fn set_dimnames(self, dimnames: SEXP) -> Self

Set the dimnames attribute; returns the same list for chaining.

Equivalent to R’s SET_DIMNAMES(x, n).

pub fn set_levels(self, levels: SEXP) -> Self

Set the levels attribute; returns the same list for chaining.

Equivalent to R’s SET_LEVELS(x, l).

pub fn set_class_str(self, classes: &[&str]) -> Self

Set the class attribute from a slice of class names.

This is a convenience wrapper that creates a character vector from the provided strings and sets it as the class attribute.

Example

let list = List::from_pairs(vec![("x", vec![1, 2, 3])]);
let df = list.set_class_str(&["data.frame"]);

pub fn set_data_frame_class(self) -> Self

Set class = "data.frame" using a cached class STRSXP.

Equivalent to set_class_str(&["data.frame"]) but avoids allocation.

pub fn set_names_str(self, names: &[&str]) -> Self

Set the names attribute from a slice of strings.

This is a convenience wrapper that creates a character vector from the provided strings and sets it as the names attribute.

Example

let list = List::from_values(vec![1, 2, 3]);
let named = list.set_names_str(&["a", "b", "c"]);

pub fn set_row_names_int(self, n: usize) -> Self

Set row.names for a data.frame using compact integer form.

R internally represents row.names as a compact integer vector c(NA_integer_, -n) when the row names are just 1:n. This is more memory-efficient than storing n strings.

Example

let list = List::from_pairs(vec![
    ("x", vec![1, 2, 3]),
    ("y", vec![4, 5, 6]),
])
.set_class_str(&["data.frame"])
.set_row_names_int(3);  // Row names: "1", "2", "3"

pub fn set_row_names_str(self, row_names: &[&str]) -> Self

Set row.names from a vector of strings.

Use this when you need custom row names. For simple sequential row names (1, 2, 3, …), use set_row_names_int instead.

Example

let list = List::from_pairs(vec![
    ("x", vec![1, 2, 3]),
])
.set_class_str(&["data.frame"])
.set_row_names_str(&["row_a", "row_b", "row_c"]);

pub unsafe fn set_elt(self, idx: isize, child: SEXP)

Set an element at the given index, protecting the child during insertion.

This is the safe way to insert a freshly allocated SEXP into a list. The child is protected for the duration of the SET_VECTOR_ELT call, ensuring it cannot be garbage collected.

Safety

• Must be called from the R main thread
• child must be a valid SEXP
• self must be a valid, protected VECSXP

Panics

Panics if idx is out of bounds.

Example

let scope = ProtectScope::new();
let list = List::from_raw(scope.alloc_vecsxp(n).into_raw());

for i in 0..n {
    let child = Rf_allocVector(REALSXP, 10);  // unprotected!
    list.set_elt(i, child);  // safe: protects child during insertion
}

pub unsafe fn set_elt_unchecked(self, idx: isize, child: SEXP)

Set an element without protecting the child.

Safety

In addition to the safety requirements of set_elt:

• The caller must ensure child is already protected or that no GC can occur between child allocation and this call.

Use this for performance when you know the child is already protected (e.g., it’s a child of another protected container, or you have an OwnedProtect guard for it).

pub unsafe fn set_elt_with<F>(self, idx: isize, f: F)

where F: FnOnce() -> SEXP,

Set an element using a callback that produces the child.

The callback is executed within a protection scope, so any allocations it performs are protected until insertion completes.

Safety

• Must be called from the R main thread
• self must be a valid, protected VECSXP

Example

let list = List::from_raw(scope.alloc_vecsxp(n).into_raw());

for i in 0..n {
    list.set_elt_with(i, || {
        let vec = Rf_allocVector(REALSXP, 10);
        fill_vector(vec);  // can allocate internally
        vec
    });
}

Trait Implementations

impl Debug for BuiltList

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

Formats the value using the given formatter.

impl Deref for BuiltList

type Target = List

The resulting type after dereferencing.

fn deref(&self) -> &List

Dereferences the value.

impl IntoR for BuiltList

type Error = !

The error type for fallible conversions.

fn try_into_sexp(self) -> Result<SEXP, Self::Error>

Try to convert this value to an R SEXP.

unsafe fn try_into_sexp_unchecked(self) -> Result<SEXP, Self::Error>

Try to convert to SEXP without thread safety checks.

fn into_sexp(self) -> SEXP

Convert this value to an R SEXP, panicking on error.

unsafe fn into_sexp_unchecked(self) -> SEXP

where Self: Sized,

Convert to SEXP without thread safety checks, panicking on error.

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: 16 bytes