feat: copied code over

pkg/iterator/iterator.go

@@ -0,0 +1,86 @@
+/*
+Package "iterator"
+*/
+package iterator
+
+import "fmt"
+
+// An iterator over slices.
+type Iterator[T any] struct {
+	items []T
+	index int
+}
+
+// Create a new iterator, over a set of items.
+func Of[T any](items []T) *Iterator[T] {
+	return &Iterator[T]{items: items, index: 0}
+}
+
+// Returns the current position of the iterator.
+func (i Iterator[T]) Index() int {
+	return i.index
+}
+
+func (i Iterator[T]) Copy() *Iterator[T] {
+	return &Iterator[T]{items: i.items, index: i.index}
+}
+
+func (i *Iterator[T]) Sync(o *Iterator[T]) {
+	i.index = o.index
+}
+
+// Create a new iterator, over a set of items.
+func (i Iterator[T]) Get() (T, error) {
+	var null T
+	if i.Done() {
+		return null, fmt.Errorf("iterator is exhausted")
+	}
+
+	return i.items[i.index], nil
+}
+
+func (i Iterator[T]) MustGet() T {
+	var null T
+	if i.Done() {
+		return null
+	}
+
+	return i.items[i.index]
+}
+
+func (i *Iterator[T]) Forward() {
+	if !i.Done() {
+		i.index++
+	}
+}
+
+// Create a new iterator, over a set of items.
+func (i *Iterator[T]) Next() (T, error) {
+	item, err := i.Get()
+	if err == nil {
+		i.index++
+	}
+
+	return item, err
+}
+
+// Create a new iterator, over a set of items.
+func (i *Iterator[T]) Back() {
+	i.index = max(i.index-1, 0)
+}
+
+// Returns the current position of the iterator.
+func (i Iterator[T]) Done() bool {
+	return i.index == len(i.items)
+}
+
+func Do[T any, U any](i *Iterator[T], fn func(i *Iterator[T]) (U, error)) (U, error) {
+	i2 := i.Copy()
+
+	out, err := fn(i2)
+	if err == nil {
+		i.Sync(i2)
+	}
+
+	return out, err
+}