Trait UnitEnumFactor 

pub trait UnitEnumFactor: Sized {
    const FACTOR_LEVELS: &'static [&'static str];

    // Required methods
    fn to_factor_index(self) -> i32;
    fn from_factor_index(idx: i32) -> Option<Self>;
}

Trait implemented by unit-only enums derived via #[derive(DataFrameRow)].

Provides the level names and 1-based index needed to convert enum values into R factor SEXPs. Unlike RFactor, this trait does not require Copy or MatchArg, making it usable with DataFrameRow-derived types that only need to participate as factor columns in data frames.

Implemented automatically by #[derive(DataFrameRow)] on unit-only enums. The blanket impl<T: UnitEnumFactor> IntoR for FactorOptionVec<T> in miniextendr-api provides the actual SEXP conversion used by the companion struct’s into_data_frame method.

Safety contract

to_factor_index must return a value in 1..=FACTOR_LEVELS.len() as i32 (or NA_INTEGER for missing) to produce a valid R factor SEXP.

Required Associated Constants

const FACTOR_LEVELS: &'static [&'static str]

Ordered level names (in the same order as the enum variants).

Required Methods

fn to_factor_index(self) -> i32

Convert self to a 1-based R factor level index.

fn from_factor_index(idx: i32) -> Option<Self>

Inverse: 1-based level index → variant, or None if out of range.

Used by the enum DataFrame reader to reconstruct unit-only enum values from an R factor column. The default blanket impl delegates to the underlying RFactor::from_level_index.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl<T: RFactor + MatchArg> UnitEnumFactor for T

const FACTOR_LEVELS: &'static [&'static str] = T::CHOICES