Derive Macro AltrepInteger 

#[derive(AltrepInteger)]
{
    // Attributes available to this derive:
    #[altrep]
}

Derive macro for ALTREP integer vector data types.

Auto-implements AltrepLen, AltIntegerData, and the low-level ALTREP trait impls (Altrep, AltVec, AltInteger, InferBase).

Attributes

• #[altrep(len = "field_name")] - Specify length field (auto-detects “len” or “length”)
• #[altrep(elt = "field_name")] - For constant vectors, specify which field provides elements
• #[altrep(dataptr)] - Enable direct data-pointer access
• #[altrep(serialize)] - Enable ALTREP serialization support
• #[altrep(subset)] - Enable Extract_subset optimization
• #[altrep(no_lowlevel)] - Skip the automatic low-level trait impls

Example (Constant Vector - Zero Boilerplate!)

#[derive(ExternalPtr, AltrepInteger)]
#[altrep(elt = "value")]  // All elements return this field
pub struct ConstantIntData {
    value: i32,
    len: usize,
}

// That's it! 3 lines instead of 30!
// AltrepLen, AltIntegerData, and low-level impls are auto-generated

#[miniextendr(class = "ConstantInt")]
pub struct ConstantIntClass(pub ConstantIntData);

Example (Custom elt() - Override One Method)

#[derive(ExternalPtr, AltrepInteger)]
pub struct ArithSeqData {
    start: i32,
    step: i32,
    len: usize,
}

// Auto-generates AltrepLen and stub AltIntegerData
// Just override elt() for custom logic:
impl AltIntegerData for ArithSeqData {
    fn elt(&self, i: usize) -> i32 {
        self.start + (i as i32) * self.step
    }
}