From 585d33cafa9da3716cb4f269f1831a64eb1268a1 Mon Sep 17 00:00:00 2001
From: dudaodong <lanliddd.2007@163.com>
Date: Tue, 17 Jan 2023 16:31:44 +0800
Subject: [PATCH] feat: add Generate for create stream

---
 stream/stream.go      | 16 ++++++++++++++++
 stream/stream_test.go | 25 +++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/stream/stream.go b/stream/stream.go
index f02fd03..9bf4537 100644
--- a/stream/stream.go
+++ b/stream/stream.go
@@ -56,6 +56,22 @@ func Of[T any](elems ...T) stream[T] {
 	return FromSlice(elems)
 }
 
+// Generate stream where each element is generated by the provided generater function
+// generater function: func(args ...U) func() (item T, ok bool) {}
+func Generate[T any](generator func() func() (T, bool)) stream[T] {
+	source := make([]T, 0)
+
+	var zeroValue T
+	for next, item, ok := generator(), zeroValue, true; ok; {
+		item, ok = next()
+		if ok {
+			source = append(source, item)
+		}
+	}
+
+	return FromSlice(source)
+}
+
 // FromSlice create stream from slice.
 func FromSlice[T any](source []T) stream[T] {
 	return stream[T]{source: source}
diff --git a/stream/stream_test.go b/stream/stream_test.go
index 948ccbb..0cc41be 100644
--- a/stream/stream_test.go
+++ b/stream/stream_test.go
@@ -6,6 +6,31 @@ import (
 	"github.com/duke-git/lancet/v2/internal"
 )
 
+func TestOf(t *testing.T) {
+	assert := internal.NewAssert(t, "TestFromSlice")
+
+	stream := Of(1, 2, 3)
+	assert.Equal([]int{1, 2, 3}, stream.ToSlice())
+}
+
+func TestGenerate(t *testing.T) {
+	assert := internal.NewAssert(t, "TestFromSlice")
+
+	n := 0
+	max := 4
+
+	generator := func() func() (int, bool) {
+		return func() (int, bool) {
+			n++
+			return n, n < max
+		}
+	}
+
+	stream := Generate(generator)
+
+	assert.Equal([]int{1, 2, 3}, stream.ToSlice())
+}
+
 func TestFromSlice(t *testing.T) {
 	assert := internal.NewAssert(t, "TestFromSlice")