Add OneOf and NotOneOf

is.go

@@ -68,8 +68,8 @@ func (is *Is) Strict() *Is {
 // not equal.
 //
 // Equal does not respect type differences. If the types are different and
-// comparable (eg int32 and int64), but the values are the same, the objects
-// are considered equal.
+// comparable (eg int32 and int64), they will be compared as though they are
+// the same type.
 func (is *Is) Equal(a interface{}, b interface{}) {
 	result := isEqual(a, b)
 	if !result {
@@ -83,8 +83,8 @@ func (is *Is) Equal(a interface{}, b interface{}) {
 // equal.
 //
 // NotEqual does not respect type differences. If the types are different and
-// comparable (eg int32 and int64), but the values are different, the objects
-// are considered not equal.
+// comparable (eg int32 and int64), they will be compared as though they are
+// the same type.
 func (is *Is) NotEqual(a interface{}, b interface{}) {
 	result := isEqual(a, b)
 	if result {
@@ -94,6 +94,50 @@ func (is *Is) NotEqual(a interface{}, b interface{}) {
 	}
 }
 
+// OneOf performs a deep compare of the provided object and an array of
+// comparison objects. It fails if the first object is not equal to one of the
+// comparison objects.
+//
+// OneOf does not respect type differences. If the types are different and
+// comparable (eg int32 and int64), they will be compared as though they are
+// the same type.
+func (is *Is) OneOf(a interface{}, b ...interface{}) {
+	result := false
+	for _, o := range b {
+		result = isEqual(a, o)
+		if result {
+			break
+		}
+	}
+	if !result {
+		fail(is, "expected object '%s' to be equal to one of '%s', but got: %v and %v",
+			objectTypeName(a),
+			objectTypeNames(b), a, b)
+	}
+}
+
+// NotOneOf performs a deep compare of the provided object and an array of
+// comparison objects. It fails if the first object is equal to one of the
+// comparison objects.
+//
+// NotOneOf does not respect type differences. If the types are different and
+// comparable (eg int32 and int64), they will be compared as though they are
+// the same type.
+func (is *Is) NotOneOf(a interface{}, b ...interface{}) {
+	result := false
+	for _, o := range b {
+		result = isEqual(a, o)
+		if result {
+			break
+		}
+	}
+	if result {
+		fail(is, "expected object '%s' not to be equal to one of '%s', but got: %v and %v",
+			objectTypeName(a),
+			objectTypeNames(b), a, b)
+	}
+}
+
 // Err checks the provided error object to determine if an error is present.
 func (is *Is) Err(e error) {
 	result := isNil(e)

is_test.go

@@ -146,6 +146,8 @@ func TestIs(t *testing.T) {
 	is.False(false)
 	is.Zero(nil)
 	is.Nil((*testStruct)(nil))
+	is.OneOf(1, 2, 3, 1)
+	is.NotOneOf(1, 2, 3)
 
 	fail = func(is *Is, format string, args ...interface{}) {}
 	is.Equal((*testStruct)(nil), &testStruct{})

workers.go

@@ -1,6 +1,7 @@
 package is
 
 import (
+	"bytes"
 	"fmt"
 	"reflect"
 )
@@ -9,6 +10,22 @@ func objectTypeName(o interface{}) string {
 	return fmt.Sprintf("%T", o)
 }
 
+func objectTypeNames(o []interface{}) string {
+	if o == nil {
+		return objectTypeName(o)
+	}
+	if len(o) == 1 {
+		return objectTypeName(o[0])
+	}
+	var b bytes.Buffer
+	b.WriteString(objectTypeName(o[0]))
+	for _, e := range o[1:] {
+		b.WriteString(",")
+		b.WriteString(objectTypeName(e))
+	}
+	return b.String()
+}
+
 func isNil(o interface{}) bool {
 	if o == nil {
 		return true