feat: add iterator package

iterator/iterator.go

@@ -0,0 +1,104 @@
+// 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
+
+import "github.com/duke-git/lancet/v2/lancetconstraints"
+
+// Iterator is used to iterate over a slice of data.
+type Iterator[T any] interface {
+	HasNext() bool
+	Next() (T, bool)
+}
+
+// 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}
+}
+
+type sliceIterator[T any] struct {
+	slice []T
+	// index int
+	// step  int
+}
+
+func (iter *sliceIterator[T]) HasNext() bool {
+	if len(iter.slice) == 0 {
+		return false
+	}
+	return true
+}
+
+func (iter *sliceIterator[T]) Next() (T, bool) {
+	if len(iter.slice) == 0 {
+		var zero T
+		return zero, false
+	}
+	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
+}
+
+// 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
+// }
+
+// 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.
+func FromRange[T lancetconstraints.Number](start, end, step T) Iterator[T] {
+	if end < start {
+		panic("RangeIterator: start should be before end")
+	} else if step <= 0 {
+		panic("RangeIterator: step should be positive")
+	}
+
+	return &rangeIterator[T]{start: start, end: end, step: step}
+}
+
+type rangeIterator[T lancetconstraints.Number] struct {
+	start, end, step T
+}
+
+func (iter *rangeIterator[T]) HasNext() bool {
+	if iter.start >= iter.end {
+		return false
+	}
+	return true
+}
+
+func (iter *rangeIterator[T]) Next() (T, bool) {
+	if iter.start >= iter.end {
+		var zero T
+		return zero, false
+	}
+	num := iter.start
+	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

@@ -0,0 +1,39 @@
+// 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
+
+import (
+	"testing"
+
+	"github.com/duke-git/lancet/v2/internal"
+)
+
+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})
+		for {
+			item, _ := iter.Next()
+			if item < 4 {
+				assert.Equal(true, iter.HasNext())
+			} else {
+				assert.Equal(false, iter.HasNext())
+				break
+			}
+		}
+	})
+
+	t.Run("slice iterator next", func(t *testing.T) {
+		iter := FromSlice([]int{1, 2, 3, 4})
+		for i := 0; i < 4; i++ {
+			item, ok := iter.Next()
+			if !ok {
+				break
+			}
+			assert.Equal(i+1, item)
+		}
+	})
+}

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()
+}