From 30d798366b11466387d918db0145e7359f5710e4 Mon Sep 17 00:00:00 2001
From: donutloop <marcel.edmund.franke@gmail.com>
Date: Fri, 7 Jan 2022 13:19:27 +0100
Subject: [PATCH] Slice: find v2 (#17)

* If slice len is zero then return false
* Convert find to generic form.
* If return T is nil then no items matched the predicate func
---
 README.md           |  2 +-
 README_zh-CN.md     |  2 +-
 slice/slice.go      | 27 +++++++++++----------------
 slice/slice_test.go |  2 +-
 4 files changed, 14 insertions(+), 19 deletions(-)

diff --git a/README.md b/README.md
index 9df4975..5fbfcb2 100644
--- a/README.md
+++ b/README.md
@@ -401,7 +401,7 @@ func Drop(slice interface{}, n int) interface{} //creates a slice with `n` eleme
 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 None(slice, function interface{}) bool // return true if all the values in the slice mismatch the criteria
 func Filter [T any] (slice []T, fn func(index int, t T) bool) []T //filter slice, fn signature should be func(int, T) 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 Find[T any](slice []T, fn func(index int, t T) bool) (*T, 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 ForEach [T any] (slice []T, fn func(index int, t T)) //iterates over elements of slice and invokes function for each element, fn signature should be func(int, T ).
 func IntSlice(slice interface{}) ([]int, error) //convert value to int slice
diff --git a/README_zh-CN.md b/README_zh-CN.md
index 25990f5..37307da 100644
--- a/README_zh-CN.md
+++ b/README_zh-CN.md
@@ -401,7 +401,7 @@ func DeleteByIndex(slice interface{}, start int, end ...int) (interface{}, error
 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 None(slice, function interface{}) bool //slice中所有元素都不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{}, 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 Find[T any](slice []T, fn func(index int, t T) bool) (*T, 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 ForEach(slice, function interface{}) //遍历切片，在每个元素上执行函数，函数签名：func(index int, value interface{})
diff --git a/slice/slice.go b/slice/slice.go
index 7a1f38d..6f43f6a 100644
--- a/slice/slice.go
+++ b/slice/slice.go
@@ -167,7 +167,7 @@ func Some(slice, function interface{}) bool {
 
 // Filter iterates over elements of slice, returning an slice of all elements `signature` returns truthy for.
 // The fn signature should be func(int, T) bool.
-func Filter [T any] (slice []T, fn func(index int, t T) bool) []T {
+func Filter[T any](slice []T, fn func(index int, t T) bool) []T {
 	res := make([]T, 0, 0)
 	for i, v := range slice {
 		if fn(i, v) {
@@ -227,30 +227,25 @@ 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{}, bool) {
-	sv := sliceValue(slice)
-	fn := functionValue(function)
-
-	elemType := sv.Type().Elem()
-	if checkSliceCallbackFuncSignature(fn, elemType, reflect.ValueOf(true).Type()) {
-		panic("function param should be of type func(int, " + elemType.String() + ")" + reflect.ValueOf(true).Type().String())
+// If return T is nil then no items matched the predicate func
+func Find[T any](slice []T, fn func(index int, t T) bool) (*T, bool) {
+	if len(slice) == 0 {
+		return nil, false
 	}
 
 	index := -1
-	for i := 0; i < sv.Len(); i++ {
-		flag := fn.Call([]reflect.Value{reflect.ValueOf(i), sv.Index(i)})[0]
-		if flag.Bool() {
+	for i, v := range slice {
+		if fn(i, v) {
 			index = i
 			break
 		}
 	}
 
 	if index == -1 {
-		var none interface{}
-		return none, false
+		return nil, false
 	}
 
-	return sv.Index(index).Interface(), true
+	return &slice[index], true
 }
 
 // FlattenDeep flattens slice recursive
@@ -279,7 +274,7 @@ func flattenRecursive(value reflect.Value, result reflect.Value) reflect.Value {
 
 // ForEach iterates over elements of slice and invokes function for each element
 // The fn signature should be func(int, T ).
-func ForEach [T any] (slice []T, fn func(index int, t T)) {
+func ForEach[T any](slice []T, fn func(index int, t T)) {
 	for i, v := range slice {
 		fn(i, v)
 	}
@@ -287,7 +282,7 @@ func ForEach [T any] (slice []T, fn func(index int, t T)) {
 
 // Map creates an slice of values by running each element of `slice` thru `function`.
 // The fn signature should be func(int, T).
-func Map [T any, U any] (slice []T, fn func(index int, t T) U) []U {
+func Map[T any, U any](slice []T, fn func(index int, t T) U) []U {
 	res := make([]U, len(slice), cap(slice))
 	for i, v := range slice {
 		res[i] = fn(i, v)
diff --git a/slice/slice_test.go b/slice/slice_test.go
index c528535..3b948b1 100644
--- a/slice/slice_test.go
+++ b/slice/slice_test.go
@@ -220,7 +220,7 @@ func TestFind(t *testing.T) {
 		t.Fatal("found nothing")
 	}
 
-	if res != 2 {
+	if *res != 2 {
 		internal.LogFailedTestInfo(t, "Find", nums, 2, res)
 		t.FailNow()
 	}