feat: adding FindKey and FindKeyBy

CHANGELOG.md

@@ -2,7 +2,14 @@
 
 @samber: I sometimes forget to update this file. Ping me on [Twitter](https://twitter.com/samuelberthe) or open an issue in case of error. We need to keep a clear changelog for easier lib upgrade.
 
-## 1.22.0 (2022-07-03)
+## 1.23.0 (2022-07-04)
+
+Adding:
+
+- lo.FindKey
+- lo.FindKeyBy
+
+## 1.22.0 (2022-07-04)
 
 Adding:
 

README.md

@@ -146,6 +146,8 @@ Supported search helpers:
 - Find
 - FindIndexOf
 - FindLastIndexOf
+- FindKey
+- FindKeyBy
 - Min
 - MinBy
 - Max
@@ -1158,6 +1160,40 @@ str, index, ok := lo.FindLastIndexOf[string]([]string{"foobar"}, func(i string)
 // "", -1, false
 ```
 
+### FindKey
+
+Returns the key of the first value matching.
+
+```go
+result1, ok1 := lo.FindKey(map[string]int{"foo": 1, "bar": 2, "baz": 3}, 2)
+// "bar", true
+
+result2, ok2 := lo.FindKey(map[string]int{"foo": 1, "bar": 2, "baz": 3}, 42)
+// "", false
+
+type test struct {
+    foobar string
+}
+result3, ok3 := lo.FindKey(map[string]test{"foo": test{"foo"}, "bar": test{"bar"}, "baz": test{"baz"}}, test{"foo"})
+// "foo", true
+```
+
+### FindKeyBy
+
+Returns the key of the first element predicate returns truthy for.
+
+```go
+result1, ok1 := lo.FindKeyBy(map[string]int{"foo": 1, "bar": 2, "baz": 3}, func(k string, v int) bool {
+    return k == "foo"
+})
+// "foo", true
+
+result2, ok2 := lo.FindKeyBy(map[string]int{"foo": 1, "bar": 2, "baz": 3}, func(k string, v int) bool {
+    return false
+})
+// "", false
+```
+
 ### Min
 
 Search the minimum value of a collection.

find.go

@@ -86,6 +86,28 @@ func FindOrElse[T any](collection []T, fallback T, predicate func(T) bool) T {
 	return fallback
 }
 
+// FindKey returns the key of the first value matching.
+func FindKey[K comparable, V comparable](object map[K]V, value V) (K, bool) {
+	for k, v := range object {
+		if v == value {
+			return k, true
+		}
+	}
+
+	return Empty[K](), false
+}
+
+// FindKeyBy returns the key of the first element predicate returns truthy for.
+func FindKeyBy[K comparable, V comparable](object map[K]V, predicate func(K, V) bool) (K, bool) {
+	for k, v := range object {
+		if predicate(k, v) {
+			return k, true
+		}
+	}
+
+	return Empty[K](), false
+}
+
 // Min search the minimum value of a collection.
 func Min[T constraints.Ordered](collection []T) T {
 	var min T

find_test.go

@@ -96,6 +96,46 @@ func TestFindOrElse(t *testing.T) {
 	is.Equal(result2, "x")
 }
 
+func TestFindKey(t *testing.T) {
+	is := assert.New(t)
+
+	result1, ok1 := FindKey(map[string]int{"foo": 1, "bar": 2, "baz": 3}, 2)
+	is.Equal("bar", result1)
+	is.True(ok1)
+
+	result2, ok2 := FindKey(map[string]int{"foo": 1, "bar": 2, "baz": 3}, 42)
+	is.Equal("", result2)
+	is.False(ok2)
+
+	type test struct {
+		foobar string
+	}
+
+	result3, ok3 := FindKey(map[string]test{"foo": test{"foo"}, "bar": test{"bar"}, "baz": test{"baz"}}, test{"foo"})
+	is.Equal("foo", result3)
+	is.True(ok3)
+
+	result4, ok4 := FindKey(map[string]test{"foo": test{"foo"}, "bar": test{"bar"}, "baz": test{"baz"}}, test{"hello world"})
+	is.Equal("", result4)
+	is.False(ok4)
+}
+
+func TestFindKeyBy(t *testing.T) {
+	is := assert.New(t)
+
+	result1, ok1 := FindKeyBy(map[string]int{"foo": 1, "bar": 2, "baz": 3}, func(k string, v int) bool {
+		return k == "foo"
+	})
+	is.Equal("foo", result1)
+	is.True(ok1)
+
+	result2, ok2 := FindKeyBy(map[string]int{"foo": 1, "bar": 2, "baz": 3}, func(k string, v int) bool {
+		return false
+	})
+	is.Equal("", result2)
+	is.False(ok2)
+}
+
 func TestMin(t *testing.T) {
 	is := assert.New(t)