Slice: find nothing case (#11)

The current behavior can result into wired edge cases.

**Current behavior**

if find was unsuccessfully then it will return the first element of the
slice

**Desired behavior**

if find was unsuccessfully then it should return negative ok and a none
value

README.md

@@ -395,7 +395,7 @@ func DeleteByIndex(slice interface{}, start int, end ...int) (interface{}, error
 func Drop(slice interface{}, n int) interface{} //creates a slice with `n` elements dropped from the beginning when n > 0, or `n` elements dropped from the ending when n < 0
 func Every(slice, function interface{}) bool //return true if all of the values in the slice pass the predicate function, function signature should be func(index int, value interface{}) bool
 func Filter(slice, function interface{}) interface{} //filter slice, function signature should be func(index int, value interface{}) bool
-func Find(slice, function interface{}) interface{} //iterates over elements of slice, returning the first one that passes a truth test on function.function signature should be func(index int, value interface{}) bool .
+func Find(slice, function interface{}) (interface{}, bool) //iterates over elements of slice, returning the first one that passes a truth test on function.function signature should be func(index int, value interface{}) bool .
 func FlattenDeep(slice interface{}) interface{} //flattens slice recursive
 func IntSlice(slice interface{}) ([]int, error) //convert value to int slice
 func InterfaceSlice(slice interface{}) []interface{} //convert value to interface{} slice

README_zh-CN.md

@@ -395,7 +395,7 @@ func Difference(slice1, slice2 interface{}) interface{} //返回
 func DeleteByIndex(slice interface{}, start int, end ...int) (interface{}, error) //删除切片中start到end位置的值
 func Drop(slice interface{}, n int) interface{} //创建一个新切片，当n大于0时删除原切片前n个元素，当n小于0时删除原切片后n个元素
 func Every(slice, function interface{}) bool //slice中所有元素都符合函数条件时返回true, 否则返回false. 函数签名：func(index int, value interface{}) bool
-func Find(slice, function interface{}) interface{} //查找slice中第一个符合条件的元素，函数签名：func(index int, value interface{}) bool
+func Find(slice, function interface{}) (interface{}, bool)//查找slice中第一个符合条件的元素，函数签名：func(index int, value interface{}) bool
 func Filter(slice, function interface{}) interface{} //过滤slice, 函数签名：func(index int, value interface{}) bool
 func FlattenDeep(slice interface{}) interface{} //将slice递归为一维切片。
 func IntSlice(slice interface{}) ([]int, error) //转成int切片

slice/slice.go

@@ -197,7 +197,7 @@ func GroupBy(slice, function interface{}) (interface{}, interface{}) {
 
 // Find iterates over elements of slice, returning the first one that passes a truth test on function.
 // The function signature should be func(index int, value interface{}) bool .
-func Find(slice, function interface{}) interface{} {
+func Find(slice, function interface{}) (interface{}, bool) {
 	sv := sliceValue(slice)
 	fn := functionValue(function)
 
@@ -206,7 +206,7 @@ func Find(slice, function interface{}) interface{} {
 		panic("function param should be of type func(int, " + elemType.String() + ")" + reflect.ValueOf(true).Type().String())
 	}
 
-	var index int
+	index := -1
 	for i := 0; i < sv.Len(); i++ {
 		flag := fn.Call([]reflect.Value{reflect.ValueOf(i), sv.Index(i)})[0]
 		if flag.Bool() {
@@ -214,7 +214,13 @@ func Find(slice, function interface{}) interface{} {
 			break
 		}
 	}
-	return sv.Index(index).Interface()
+
+	if index == -1 {
+		var none interface{}
+		return none, false
+	}
+
+	return sv.Index(index).Interface(), true
 }
 
 // FlattenDeep flattens slice recursive

slice/slice_test.go

@@ -190,13 +190,28 @@ func TestFind(t *testing.T) {
 	even := func(i, num int) bool {
 		return num%2 == 0
 	}
-	res := Find(nums, even)
+	res, ok := Find(nums, even)
+	if !ok {
+		t.Fatal("found nothing")
+	}
+
 	if res != 2 {
 		internal.LogFailedTestInfo(t, "Find", nums, 2, res)
 		t.FailNow()
 	}
 }
 
+func TestFindFoundNothing(t *testing.T) {
+	nums := []int{1, 1, 1, 1, 1, 1}
+	findFunc := func(i, num int) bool {
+		return num > 1
+	}
+	_, ok := Find(nums, findFunc)
+	if ok {
+		t.Fatal("found something")
+	}
+}
+
 func TestFlattenDeep(t *testing.T) {
 	input := [][][]string{{{"a", "b"}}, {{"c", "d"}}}
 	expected := []string{"a", "b", "c", "d"}