Struct IndexSpec 

pub struct IndexSpec<T> {
    pub column: &'static str,
    pub extractor: fn(&T) -> Option<String>,
    pub unique: bool,
}

Specification for a single secondary column peeled out of T at write time. All peeled columns are typed TEXT in SQLite; None from the extractor becomes SQL NULL.

Fields

column: &'static str

Column name. Must be a valid SQL identifier (a-z, A-Z, 0-9, _) and is splat directly into the generated DDL, so this MUST be a compile-time string literal.

extractor: fn(&T) -> Option<String>

Extractor pulling the column value out of T. None is written as SQL NULL.

unique: bool

If true, column is included in a table-level UNIQUE(...) constraint. SQLite treats NULLs as distinct in UNIQUE, so nullable unique columns only enforce uniqueness among non-NULL values. Callers needing “unique including NULL” must enforce it in application code (see environments.rs for the pattern).