Struct ListBuilder 

pub struct ListBuilder<'a> {
    list: SEXP,
    _scope: &'a ProtectScope,
}

Builder for constructing lists with efficient protection management.

ListBuilder holds a reference to a ProtectScope, allowing multiple elements to be inserted without repeatedly protecting/unprotecting each one. This is more efficient than using List::set_elt in a loop.

Example

unsafe fn build_list(n: isize) -> SEXP {
    let scope = ProtectScope::new();
    let builder = ListBuilder::new(&scope, n);

    for i in 0..n {
        // Allocations inside the loop are protected by the scope
        let child = scope.alloc_real(10).into_raw();
        builder.set(i, child);
    }

    builder.into_sexp()
}

Fields

list: SEXP

_scope: &'a ProtectScope

Implementations

impl<'a> ListBuilder<'a>

pub unsafe fn new(scope: &'a ProtectScope, len: usize) -> Self

Create a new list builder with the given length.

The list is allocated and protected using the provided scope.

Safety

Must be called from the R main thread.

pub unsafe fn from_protected(scope: &'a ProtectScope, list: SEXP) -> Self

Create a builder wrapping an existing protected list.

Safety

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

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

Set an element at the given index.

The child should be protected by the same scope (or a parent scope). Use scope.protect_raw(...) before calling this method.

Safety

• child must be a valid SEXP
• child should be protected (typically via the same scope)

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

Set an element, protecting the child within the builder’s scope.

This is a convenience method that protects the child and then inserts it.

Safety

• child must be a valid SEXP

pub fn as_sexp(&self) -> SEXP

Get the underlying list SEXP.

pub fn into_list(self) -> List

Convert to a List wrapper.

pub fn into_sexp(self) -> SEXP

Convert to the underlying SEXP.

pub fn len(&self) -> isize

Get the length of the list.

pub fn is_empty(&self) -> bool

Check if the list is empty.