structure: remove returning error, it should panic just like reflect

package

README.md

@@ -31,10 +31,7 @@ s := &Server{
 Convert to a `map[string]interface{}`
 
 ```go
-m, err := structure.ToMap(s)
-if err != nil {
-	panic(err)
-}
+m := structure.ToMap(s)
 
 // prints: map[string]interface {}{"Name":"Arslan", "ID":123456, "Enabled":true}
 fmt.Printf("%#v", m)
@@ -46,10 +43,7 @@ Convert to a `[]interface{}`. Slice values are **sorted** by default according
 to the field names.
 
 ```go
-m, err := structure.ToSlice(s)
-if err != nil {
-	panic(err)
-}
+m := structure.ToSlice(s)
 
 // prints: []interface {}{true, 123456, "Arslan"}
 fmt.Printf("%#v", m)

structure.go

@@ -2,19 +2,16 @@
 package structure
 
 import (
-	"errors"
 	"reflect"
 	"sort"
 )
 
-// ErrNotStruct is returned when the passed value is not a struct
-var ErrNotStruct = errors.New("not struct")
-
-// ToMap converts a struct to a map[string]interface{}. The default map key
-// string is the struct fieldname but this can be changed by defining a
-// "structure" tag key if needed. Note that only exported fields of a struct
-// can be accessed, non exported fields will be neglected.
-func ToMap(s interface{}) (map[string]interface{}, error) {
+// ToMap converts the given s struct to a map[string]interface{}. The default
+// map key names are the struct fieldnames but this can be changed by defining
+// a "structure" tag key if needed. Note that only exported fields of a struct
+// can be accessed, non exported fields will be neglected. It panics if s's
+// kind is not struct.
+func ToMap(s interface{}) map[string]interface{} {
 	out := make(map[string]interface{})
 
 	t := reflect.TypeOf(s)
@@ -27,7 +24,7 @@ func ToMap(s interface{}) (map[string]interface{}, error) {
 	}
 
 	if t.Kind() != reflect.Struct {
-		return nil, ErrNotStruct
+		panic("not struct")
 	}
 
 	for i := 0; i < t.NumField(); i++ {
@@ -48,17 +45,15 @@ func ToMap(s interface{}) (map[string]interface{}, error) {
 		out[name] = v.Field(i).Interface()
 	}
 
-	return out, nil
+	return out
 }
 
-// ToSlice converts a struct's field values to a []interface{}. Values are
-// inserted and sorted according to the field names. Note that only exported
-// fields of a struct can be accessed, non exported fields  will be neglected.
-func ToSlice(s interface{}) ([]interface{}, error) {
-	m, err := ToMap(s)
-	if err != nil {
-		return nil, err
-	}
+// ToSlice converts the given s struct's field values to a []interface{}.
+// Values are inserted and sorted according to the field names. Note that only
+// exported fields of a struct can be accessed, non exported fields  will be
+// neglected.  It panics if s's kind is not struct.
+func ToSlice(s interface{}) []interface{} {
+	m := ToMap(s)
 
 	keys := make([]string, len(m))
 	count := 0
@@ -75,10 +70,26 @@ func ToSlice(s interface{}) ([]interface{}, error) {
 		t[i] = m[key]
 	}
 
-	return t, nil
+	return t
 
 }
 
+// Fields returns a sorted slice of field names.
+func Fields(s interface{}) []string {
+	m := ToMap(s)
+
+	keys := make([]string, len(m))
+	count := 0
+	for k := range m {
+		keys[count] = k
+		count++
+	}
+
+	sort.Strings(keys)
+
+	return keys
+}
+
 // IsStruct returns true if the given variable is a struct or a pointer to
 // struct.
 func IsStruct(s interface{}) bool {

structure_example_test.go

@@ -15,10 +15,7 @@ func ExampleToMap() {
 		Enabled: true,
 	}
 
-	m, err := ToMap(s)
-	if err != nil {
-		panic(err)
-	}
+	m := ToMap(s)
 
 	fmt.Printf("%#v\n", m["Name"])
 	fmt.Printf("%#v\n", m["ID"])
@@ -43,10 +40,7 @@ func ExampleToMap_tags() {
 		ID:   789012,
 	}
 
-	m, err := ToMap(s)
-	if err != nil {
-		panic(err)
-	}
+	m := ToMap(s)
 
 	// access them by the custom tags defined above
 	fmt.Printf("%#v\n", m["server_name"])
@@ -72,10 +66,7 @@ func ExampleToSlice() {
 		Enabled: false,
 	}
 
-	m, err := ToSlice(s)
-	if err != nil {
-		panic(err)
-	}
+	m := ToSlice(s)
 
 	// note that the output is sorted according to the field names
 	fmt.Printf("%#v\n", m)

structure_test.go

@@ -8,11 +8,15 @@ import (
 func TestToMapNonStruct(t *testing.T) {
 	foo := []string{"foo"}
 
-	_, err := ToMap(foo)
-	if err == nil {
-		t.Error("ToMap shouldn't accept non struct types")
-	}
+	defer func() {
+		err := recover()
+		if err == nil {
+			t.Error("Passing a non struct into ToMap should panic")
+		}
+	}()
 
+	// this should panic. We are going to recover and and test it
+	_ = ToMap(foo)
 }
 
 func TestToMap(t *testing.T) {
@@ -26,10 +30,7 @@ func TestToMap(t *testing.T) {
 		C: true,
 	}
 
-	a, err := ToMap(T)
-	if err != nil {
-		t.Error(err)
-	}
+	a := ToMap(T)
 
 	if typ := reflect.TypeOf(a).Kind(); typ != reflect.Map {
 		t.Errorf("ToMap should return a map type, got: %v", typ)
@@ -69,19 +70,14 @@ func TestToMap_Tag(t *testing.T) {
 		C: true,
 	}
 
-	a, err := ToMap(T)
-	if err != nil {
-		t.Error(err)
-	}
+	a := ToMap(T)
 
 	inMap := func(key interface{}) bool {
 		for k := range a {
 			if reflect.DeepEqual(k, key) {
-
 				return true
 			}
 		}
-
 		return false
 	}
 
@@ -117,10 +113,7 @@ func TestToSlice(t *testing.T) {
 		C: true,
 	}
 
-	s, err := ToSlice(T)
-	if err != nil {
-		t.Error(err)
-	}
+	s := ToSlice(T)
 
 	inSlice := func(val interface{}) bool {
 		for _, v := range s {
@@ -128,7 +121,6 @@ func TestToSlice(t *testing.T) {
 				return true
 			}
 		}
-
 		return false
 	}