feat: add Concat for stream

stream/stream.go

@@ -43,7 +43,7 @@ import (
 
 // 	// part of methods custom extension
 // 	Reverse() StreamI[T]
-// 	Range(start, end int64) StreamI[T]
+// 	Range(start, end int) StreamI[T]
 // 	Concat(streams ...StreamI[T]) StreamI[T]
 // }
 
@@ -72,12 +72,12 @@ func Generate[T any](generator func() func() (item T, ok bool)) stream[T] {
 	return FromSlice(source)
 }
 
-// FromSlice create stream from slice.
+// FromSlice creates stream from slice.
 func FromSlice[T any](source []T) stream[T] {
 	return stream[T]{source: source}
 }
 
-// FromChannel create stream from channel.
+// FromChannel creates stream from channel.
 func FromChannel[T any](source <-chan T) stream[T] {
 	s := make([]T, 0)
 
@@ -88,7 +88,7 @@ func FromChannel[T any](source <-chan T) stream[T] {
 	return FromSlice(s)
 }
 
-// FromRange create a number stream from start to end. both start and end are included. [start, end]
+// FromRange creates a number stream from start to end. both start and end are included. [start, end]
 func FromRange[T constraints.Integer | constraints.Float](start, end, step T) stream[T] {
 	if end < start {
 		panic("stream.FromRange: param start should be before param end")
@@ -106,6 +106,16 @@ func FromRange[T constraints.Integer | constraints.Float](start, end, step T) st
 	return FromSlice(source)
 }
 
+// Concat creates a lazily concatenated stream whose elements are all the elements of the first stream followed by all the elements of the second stream.
+func Concat[T any](a, b stream[T]) stream[T] {
+	source := make([]T, 0)
+
+	source = append(source, a.source...)
+	source = append(source, b.source...)
+
+	return FromSlice(source)
+}
+
 // Distinct returns a stream that removes the duplicated items.
 func (s stream[T]) Distinct() stream[T] {
 	source := make([]T, 0)
@@ -255,6 +265,53 @@ func (s stream[T]) Count() int {
 	return len(s.source)
 }
 
+// FindFirst returns the first element of this stream and true, or zero value and false if the stream is empty.
+func (s stream[T]) FindFirst() (T, bool) {
+	var result T
+
+	if s.source == nil || len(s.source) == 0 {
+		return result, false
+	}
+
+	return s.source[0], true
+}
+
+// Reverse returns a stream whose elements are reverse order of given stream.
+func (s stream[T]) Reverse() stream[T] {
+	l := len(s.source)
+	source := make([]T, l)
+
+	for i := 0; i < l; i++ {
+		source[i] = s.source[l-1-i]
+	}
+	return FromSlice(source)
+}
+
+// Range returns a stream whose elements are in the range from start(included) to end(excluded) original stream.
+func (s stream[T]) Range(start, end int) stream[T] {
+	if start < 0 {
+		start = 0
+	}
+	if end < 0 {
+		end = 0
+	}
+	if start >= end {
+		return FromSlice([]T{})
+	}
+
+	source := make([]T, 0)
+
+	if end > len(s.source) {
+		end = len(s.source)
+	}
+
+	for i := start; i < end; i++ {
+		source = append(source, s.source[i])
+	}
+
+	return FromSlice(source)
+}
+
 // ToSlice return the elements in the stream.
 func (s stream[T]) ToSlice() []T {
 	return s.source

stream/stream_test.go

@@ -247,3 +247,59 @@ func TestStream_Reduce(t *testing.T) {
 
 	assert.Equal(6, result)
 }
+
+func TestStream_FindFirst(t *testing.T) {
+	assert := internal.NewAssert(t, "TestStream_FindFirst")
+
+	stream := FromSlice([]int{1, 2, 3})
+
+	result, ok := stream.FindFirst()
+
+	assert.Equal(1, result)
+	assert.Equal(true, ok)
+}
+
+func TestStream_Reverse(t *testing.T) {
+	assert := internal.NewAssert(t, "TestStream_Reverse")
+
+	s := FromSlice([]int{1, 2, 3})
+
+	rs := s.Reverse()
+
+	assert.Equal([]int{3, 2, 1}, rs.ToSlice())
+}
+
+func TestStream_Range(t *testing.T) {
+	assert := internal.NewAssert(t, "TestStream_Range")
+
+	s := FromSlice([]int{1, 2, 3})
+
+	s1 := s.Range(-1, 0)
+	assert.Equal([]int{}, s1.ToSlice())
+
+	s2 := s.Range(0, -1)
+	assert.Equal([]int{}, s2.ToSlice())
+
+	s3 := s.Range(0, 0)
+	assert.Equal([]int{}, s3.ToSlice())
+
+	s4 := s.Range(1, 1)
+	assert.Equal([]int{}, s4.ToSlice())
+
+	s5 := s.Range(0, 1)
+	assert.Equal([]int{1}, s5.ToSlice())
+
+	s6 := s.Range(0, 4)
+	assert.Equal([]int{1, 2, 3}, s6.ToSlice())
+}
+
+func TestStream_Concat(t *testing.T) {
+	assert := internal.NewAssert(t, "TestStream_Concat")
+
+	s1 := FromSlice([]int{1, 2, 3})
+	s2 := FromSlice([]int{4, 5, 6})
+
+	s := Concat(s1, s2)
+
+	assert.Equal([]int{1, 2, 3, 4, 5, 6}, s.ToSlice())
+}