//! Binding relations: rows over named (variable) columns.
//!
//! Every operator in this crate (after the initial atom scan) consumes and
//! produces [`Relation`]s. Column names are variable names; a value at column
//! `i` of a row is the value bound to variable `columns[i]` in that solution.

use crate::value::Value;

#[derive(Debug, Clone)]
pub struct Relation {
    pub columns: Vec<String>,
    pub rows: Vec<Vec<Value>>,
}

impl Relation {
    #[must_use]
    pub fn new(columns: Vec<String>) -> Self {
        Self {
            columns,
            rows: Vec::new(),
        }
    }

    /// # Panics
    /// Panics if `row.len() != self.columns.len()`.
    pub fn push(&mut self, row: Vec<Value>) {
        assert_eq!(
            row.len(),
            self.columns.len(),
            "row arity mismatch: expected {}, got {}",
            self.columns.len(),
            row.len(),
        );
        self.rows.push(row);
    }
}