feat: update iterator package

iterator/iterator.go

@@ -1,68 +1,144 @@
-// Copyright 2021 dudaodong@gmail.com. All rights resulterved.
+// Copyright 2022 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 provides a way to iterate over values stored in containers.
+// note:
+// 1. Full feature iterator is complicated, this pacakge is just a experiment to explore how iterators could work in Go.
+// 2. The functionality of this package is very simple and limited, may not meet the actual dev needs.
+// 3. It is currently under development, unstable, and will not be completed for some time in the future.
+// So, based on above factors, you may not use it in production. but, anyone is welcome to improve it.
+// Hope that Go can support iterator in future. see https://github.com/golang/go/discussions/54245 and https://github.com/golang/go/discussions/56413
 package iterator
 
 import "github.com/duke-git/lancet/v2/lancetconstraints"
 
-// Iterator is used to iterate over a slice of data.
+// Iterator supports iterating over a sequence of values of type `E`.
 type Iterator[T any] interface {
+	// Next checks if there is a next value in the iteration or not
 	HasNext() bool
-	Next() (T, bool)
+	// Next returns the next value in the iteration if there is one,
+	// and reports whether the returned value is valid.
+	// Once Next returns ok==false, the iteration is over,
+	// and all subsequent calls will return ok==false.
+	Next() (item T, ok bool)
 }
 
+// StopIterator is an  interface for stopping Iterator.
+type StopIterator[T any] interface {
+	Iterator[T]
+
+	// Stop indicates that the iterator will no longer be used.
+	// After a call to Stop, future calls to Next may panic.
+	// Stop may be called multiple times;
+	// all calls after the first will have no effect.
+	Stop()
+}
+
+// DeleteIter is an Iter that implements a Delete method.
+type DeleteIterator[T any] interface {
+	Iterator[T]
+
+	// Delete deletes the current iterator element;
+	// that is, the one returned by the last call to Next.
+	// Delete should panic if called before Next or after
+	// Next returns false.
+	Delete()
+}
+
+// SetIterator is an Iter that implements a Set method.
+type SetIterator[T any] interface {
+	Iterator[T]
+
+	// Set replaces the current iterator element with v.
+	// Set should panic if called before Next or after
+	// Next returns false.
+	Set(v T)
+}
+
+// PrevIterator is an iterator with a Prev method.
+type PrevIterator[T any] interface {
+	Iterator[T]
+
+	// Prev moves the iterator to the previous position.
+	// After calling Prev, Next will return the value at
+	// that position in the container. For example, after
+	//   it.Next() returning (v, true)
+	//   it.Prev()
+	// another call to it.Next will again return (v, true).
+	// Calling Prev before calling Next may panic.
+	// Calling Prev after Next returns false will move
+	// to the last element, or, if there are no elements,
+	// to the iterator's initial state.
+	Prev()
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+// Functions that create an Iterator from some other type.                                       //
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
 // FromSlice returns an iterator over a slice of data.
-func FromSlice[T any](data []T) Iterator[T] {
-	// return &sliceIterator[T]{slice: data, index: 0, step: 1}
-	return &sliceIterator[T]{slice: data}
+func FromSlice[T any](slice []T) Iterator[T] {
+	return &sliceIterator[T]{slice: slice, index: -1}
+}
+
+func ToSlice[T any](iter Iterator[T]) []T {
+	result := []T{}
+	for item, ok := iter.Next(); ok; item, ok = iter.Next() {
+		result = append(result, item)
+	}
+	return result
 }
 
 type sliceIterator[T any] struct {
 	slice []T
-	// index int
-	// step  int
+	index int
 }
 
 func (iter *sliceIterator[T]) HasNext() bool {
-	if len(iter.slice) == 0 {
-		return false
-	}
-	return true
+	return iter.index < len(iter.slice)-1
 }
 
 func (iter *sliceIterator[T]) Next() (T, bool) {
-	if len(iter.slice) == 0 {
-		var zero T
-		return zero, false
+	iter.index++
+	ok := iter.index >= 0 && iter.index < len(iter.slice)
+	var item T
+	if ok {
+		item = iter.slice[iter.index]
 	}
-	item := iter.slice[0]
-	iter.slice = iter.slice[1:]
-	return item, true
+	return item, ok
+
+	// if len(iter.slice) == 0 {
+	// 	var zero T
+	// 	return zero, false
+	// }
+	// iter.index++
+	// item := iter.slice[0]
+	// iter.slice = iter.slice[1:]
+	// return item, true
 }
 
-// Count
-func (iter *sliceIterator[T]) Count() int {
-	count := len(iter.slice)
-	iter.slice = []T{}
-	return count
+// Prev implements PrevIterator.
+func (iter *sliceIterator[T]) Prev() {
+	if iter.index == -1 {
+		panic("Next function should be called Prev")
+	}
+	if iter.HasNext() {
+		iter.index--
+	} else {
+		iter.index = len(iter.slice) - 1
+	}
 }
 
-// func (iter *sliceIterator[T]) Begin(data []T) Iterator[T] {
-// 	iter.data = data
-// 	iter.index = 0
-// 	iter.step = 1
-
-// 	return iter
-// }
-
-// func (iter *sliceIterator[T]) End(data []T) Iterator[T] {
-// 	iter.data = data
-// 	iter.index = len(data)
-// 	iter.step = 1
-
-// 	return iter
-// }
+// Set implements SetIterator.
+func (iter *sliceIterator[T]) Set(value T) {
+	if iter.index == -1 {
+		panic("Next function should be called Set")
+	}
+	if iter.index >= len(iter.slice) || len(iter.slice) == 0 {
+		panic("No element in current iterator")
+	}
+	iter.slice[iter.index] = value
+}
 
 // FromRange creates a iterator which returns the numeric range between start inclusive and end
 // exclusive by the step size. start should be less than end, step shoud be positive.
@@ -96,9 +172,3 @@ func (iter *rangeIterator[T]) Next() (T, bool) {
 	iter.start += iter.step
 	return num, true
 }
-
-func (iter *rangeIterator[T]) Count() int {
-	count := (iter.end - iter.start) / iter.step
-	iter.start = iter.end
-	return int(count)
-}

iterator/iterator_test.go

@@ -1,4 +1,4 @@
-// Copyright 2021 dudaodong@gmail.com. All rights resulterved.
+// Copyright 2022 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
@@ -13,27 +13,38 @@ import (
 func TestSliceIterator(t *testing.T) {
 	assert := internal.NewAssert(t, "TestSliceIterator")
 
-	t.Run("slice iterator has next", func(t *testing.T) {
-		iter := FromSlice([]int{1, 2, 3, 4})
+	// HashNext
+	t.Run("slice iterator HasNext: ", func(t *testing.T) {
+		iter1 := FromSlice([]int{1, 2, 3, 4})
 		for {
-			item, _ := iter.Next()
-			if item < 4 {
-				assert.Equal(true, iter.HasNext())
-			} else {
-				assert.Equal(false, iter.HasNext())
+			item, _ := iter1.Next()
+
+			if item == 4 {
+				assert.Equal(false, iter1.HasNext())
 				break
+			} else {
+				assert.Equal(true, iter1.HasNext())
 			}
 		}
+
+		iter2 := FromSlice([]int{})
+		assert.Equal(false, iter2.HasNext())
 	})
 
-	t.Run("slice iterator next", func(t *testing.T) {
-		iter := FromSlice([]int{1, 2, 3, 4})
+	//Next
+	t.Run("slice iterator Next: ", func(t *testing.T) {
+		iter1 := FromSlice([]int{1, 2, 3, 4})
 		for i := 0; i < 4; i++ {
-			item, ok := iter.Next()
+			item, ok := iter1.Next()
 			if !ok {
 				break
 			}
 			assert.Equal(i+1, item)
 		}
+
+		iter2 := FromSlice([]int{})
+		_, ok := iter2.Next()
+		assert.Equal(false, ok)
 	})
+
 }

iterator/operation.go

@@ -1,7 +1,13 @@
-// Copyright 2021 dudaodong@gmail.com. All rights resulterved.
+// Copyright 2022 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 provides a way to iterate over values stored in containers.
+// note:
+// 1. Full feature iterator is complicated, this pacakge is just a experiment to explore how iterators could work in Go.
+// 2. The functionality of this package is very simple and limited, may not meet the actual dev needs.
+// 3. It is currently under development, unstable, and will not be completed for some time in the future.
+// So, based on above factors, you may not use it in production. but, anyone is welcome to improve it.
+// Hope that Go can support iterator in future. see https://github.com/golang/go/discussions/54245 and https://github.com/golang/go/discussions/56413
 package iterator
 
 // Map creates a new iterator which applies a function to all items of input iterator.