Merge branch 'feature/filter-map'

Author: Tom Godkin

iter/filter.go

@@ -36,3 +36,30 @@ func Exclude[T any](iter Iterator[T], fun func(T) bool) *FilterIter[T] {
 	inverse := func(t T) bool { return !fun(t) }
 	return &FilterIter[T]{iter, inverse}
 }
+
+type FilterMapIter[T any, U any] struct {
+	itr Iterator[T]
+	fn  func(T) option.Option[U]
+}
+
+func (flt *FilterMapIter[T, U]) Next() option.Option[U] {
+	for {
+		val, ok := flt.itr.Next().Value()
+		if !ok {
+			return option.None[U]()
+		}
+		result := flt.fn(val)
+		if result.IsSome() {
+			return result
+		}
+	}
+}
+
+var _ Iterator[struct{}] = new(FilterMapIter[struct{}, struct{}])
+
+// Accepts an underlying iterator as data source and a filtering + mapping function
+// it allows the user to filter elements by returning a None variant and to transform
+// elements by returning a Some variant.
+func FilterMap[T any, U any](itr Iterator[T], fun func(T) option.Option[U]) Iterator[U] {
+	return &FilterMapIter[T, U]{itr, fun}
+}

iter/filter_test.go

@@ -7,6 +7,7 @@ import (
 	"github.com/BooleanCat/go-functional/internal/assert"
 	"github.com/BooleanCat/go-functional/iter"
 	"github.com/BooleanCat/go-functional/iter/filters"
+	"github.com/BooleanCat/go-functional/option"
 )
 
 func ExampleFilter() {
@@ -21,6 +22,24 @@ func ExampleFilter() {
 	// None
 }
 
+func ExampleFilterMap() {
+	selectAndTripleOdds := func(x int) option.Option[int] {
+		if x%2 == 0 {
+			return option.None[int]()
+		}
+		return option.Some(x * 3)
+	}
+
+	triples := iter.FilterMap[int](
+		iter.Take[int](iter.Count(), 6),
+		selectAndTripleOdds,
+	)
+
+	fmt.Println(iter.Collect(triples))
+
+	// Output: [3 9 15]
+}
+
 func ExampleExclude() {
 	filtered := iter.Exclude[int](iter.Lift([]int{0, 1, 0, 2}), filters.IsZero[int])
 	fmt.Println(filtered.Next())
@@ -52,3 +71,38 @@ func TestExclude(t *testing.T) {
 	assert.Equal(t, evens.Next().Unwrap(), 1)
 	assert.Equal(t, evens.Next().Unwrap(), 3)
 }
+
+func TestFilterMap(t *testing.T) {
+	selectEvenAndDouble := func(x int) option.Option[int] {
+		if x%2 > 0 {
+			return option.None[int]()
+		}
+
+		return option.Some(x * 2)
+	}
+
+	fltMap := iter.FilterMap[int](
+		iter.Lift([]int{1, 2, 3, 4, 5, 6}),
+		selectEvenAndDouble,
+	)
+	result := iter.Collect(fltMap)
+
+	assert.SliceEqual(t, result, []int{4, 8, 12})
+}
+
+func TestFilterMapEmpty(t *testing.T) {
+	selectEvenAndDouble := func(x int) option.Option[int] {
+		if x%2 > 0 {
+			return option.None[int]()
+		}
+
+		return option.Some(x * 2)
+	}
+
+	fltMapEmpty := iter.FilterMap[int](
+		iter.Exhausted[int](),
+		selectEvenAndDouble,
+	)
+
+	assert.Empty(t, iter.Collect(fltMapEmpty))
+}