Function execute_expression_selection

crates/gitql-engine/src/engine_executor.rs:171–212

(
    env: &mut Environment,
    selected_rows: &mut [Row],
    object_titles: &[String],
    selected_expr_titles: &[String],
    selected_expr: &[Box<dyn Expr>],
)

#[inline(always)]
fn execute_expression_selection(
    env: &mut Environment,
    selected_rows: &mut [Row],
    object_titles: &[String],
    selected_expr_titles: &[String],
    selected_expr: &[Box<dyn Expr>],
) -> Result<(), String> {
    // Cache the index of each expression position to provide fast insertion
    let mut titles_index_map: HashMap<String, usize> = HashMap::new();
    for expr_column_title in selected_expr_titles {
        let expr_title_index = object_titles
            .iter()
            .position(|r| r.eq(expr_column_title))
            .unwrap();
        titles_index_map.insert(expr_column_title.to_string(), expr_title_index);
    }

    for row in selected_rows.iter_mut() {
        for (index, expr) in selected_expr.iter().enumerate() {
            let expr_title = &selected_expr_titles[index];
            let value_index = *titles_index_map.get(expr_title).unwrap();

            if index < row.values.len() && !row.values[value_index].is_null() {
                continue;
            }

            // Ignore evaluating expression if it symbol, that mean it a reference to aggregated value or function
            let value = if expr.kind() == ExprKind::Symbol {
                Box::new(NullValue)
            } else {
                evaluate_expression(env, expr, object_titles, &row.values)?
            };

            if index >= row.values.len() {
                row.values.push(value);
            } else {
                row.values[value_index] = value;
            }
        }
    }
    Ok(())
}

fn execute_where_statement(
    env: &mut Environment,