groupjoin.go

package linq

type groupJoinEnumerator[S1, S2, T any, K comparable] struct {
	eOut  Enumerator[S1]
	eIn   Enumerator[S2]
	ksOut func(S1) (K, error)
	ksIn  func(S2) (K, error)
	rSel  func(S1, Enumerable[S2]) (T, error)

	ms2 *hashMap[K, S2]
}

// GroupJoin correlates the elements of two sequences based on equality of keys and groups the results.
func GroupJoin[S1, S2, T any, K comparable, E1 IEnumerable[S1], E2 IEnumerable[S2]](
	outer E1,
	inner E2,
	outerKeySelector func(S1) (K, error),
	innerKeySelector func(S2) (K, error),
	resultSelector func(S1, Enumerable[S2]) (T, error),
) Enumerable[T] {
	return func() Enumerator[T] {
		return &groupJoinEnumerator[S1, S2, T, K]{
			eOut:  outer(),
			eIn:   inner(),
			ksOut: outerKeySelector,
			ksIn:  innerKeySelector,
			rSel:  resultSelector,
		}
	}
}

func (e *groupJoinEnumerator[S1, S2, T, K]) Next() (def T, _ error) {
	out, err := e.eOut.Next()
	if err != nil {
		return def, err
	}
	if e.ms2 == nil {
		e.ms2 = newHashMap(e.ksIn, alwaysNotEqual[S2])
		if err := e.ms2.addAll(e.eIn); err != nil {
			return def, err
		}
	}
	k, err := e.ksOut(out)
	if err != nil {
		return def, err
	}

	return e.rSel(out, FromSlice(e.ms2.gets(k)))
}