Method flat_map

src/transform/src/analysis.rs:1595–1610

(&self, tf: &TableFunc, input: CardinalityEstimate)

    // We split it up into functions to make it all a bit more tractable to work with.
    impl Cardinality {
        fn flat_map(&self, tf: &TableFunc, input: CardinalityEstimate) -> CardinalityEstimate {
            match tf {
                TableFunc::Wrap { types, width } => {
                    // DBZ is harmless (produces inf, empty estimate), but still a broken invariant
                    if *width == 0 {
                        error!("cardinality estimation encountered TableFunc::Wrap with width 0");
                    }

                    input * (f64::cast_lossy(types.len()) / f64::cast_lossy(*width))
                }
                _ => {
                    // TODO(mgree) what explosion factor should we make up?
                    input * CardinalityEstimate::from(4.0)
                }
            }
        }

        fn predicate(
            &self,