feat: add iterator package

iterator/operation.go

@@ -0,0 +1,55 @@
+// Copyright 2021 dudaodong@gmail.com. All rights resulterved.
+// Use of this source code is governed by MIT license
+
+// Package iterator implements some feature of C++ STL iterators
+package iterator
+
+// Map creates a new iterator which applies a function to all items of input iterator.
+func Map[T any, U any](iter Iterator[T], iteratee func(item T) U) Iterator[U] {
+	return &mapIterator[T, U]{
+		iter:     iter,
+		iteratee: iteratee,
+	}
+}
+
+type mapIterator[T any, U any] struct {
+	iter     Iterator[T]
+	iteratee func(T) U
+}
+
+func (mr *mapIterator[T, U]) HasNext() bool {
+	return mr.iter.HasNext()
+}
+
+func (mr *mapIterator[T, U]) Next() (U, bool) {
+	var zero U
+	item, ok := mr.iter.Next()
+	if !ok {
+		return zero, false
+	}
+	return mr.iteratee(item), true
+}
+
+// Filter creates a new iterator that returns only the items that pass specified predicate function.
+func Filter[T any](iter Iterator[T], predicateFunc func(item T) bool) Iterator[T] {
+	return &filterIterator[T]{iter: iter, predicateFunc: predicateFunc}
+}
+
+type filterIterator[T any] struct {
+	iter          Iterator[T]
+	predicateFunc func(T) bool
+}
+
+func (fr *filterIterator[T]) Next() (T, bool) {
+	for item, ok := fr.iter.Next(); ok; item, ok = fr.iter.Next() {
+		if fr.predicateFunc(item) {
+			return item, true
+		}
+	}
+	var zero T
+	return zero, false
+}
+
+func (fr *filterIterator[T]) HasNext() bool {
+	return fr.iter.HasNext()
+}