Merge pull request #38 from mammothbane/master

add Zero function to field

field.go

@@ -84,6 +84,13 @@ func (f *Field) Set(val interface{}) error {
 	return nil
 }
 
+// Zero sets the field to its zero value. It returns an error if the field is not
+// settable (not addressable or not exported).
+func (f *Field) Zero() error {
+	zero := reflect.Zero(f.value.Type()).Interface()
+	return f.Set(zero)
+}
+
 // Fields returns a slice of Fields. This is particular handy to get the fields
 // of a nested struct . A struct tag with the content of "-" ignores the
 // checking of that particular field. Example:

field_test.go

@@ -133,6 +133,65 @@ func TestField_Set(t *testing.T) {
 	}
 }
 
+func TestField_Zero(t *testing.T) {
+	s := newStruct()
+
+	f := s.Field("A")
+	err := f.Zero()
+	if err != nil {
+		t.Error(err)
+	}
+
+	if f.Value().(string) != "" {
+		t.Errorf("Zeroed value is wrong: %s want: %s", f.Value().(string), "")
+	}
+
+	f = s.Field("Y")
+	err = f.Zero()
+	if err != nil {
+		t.Error(err)
+	}
+
+	sliceLen := len(f.Value().([]string))
+	if sliceLen != 0 {
+		t.Errorf("Zeroed values slice length is wrong: %d, want: %d", sliceLen, 0)
+	}
+
+	f = s.Field("C")
+	err = f.Zero()
+	if err != nil {
+		t.Error(err)
+	}
+
+	if f.Value().(bool) {
+		t.Errorf("Zeroed value is wrong: %t want: %t", f.Value().(bool), false)
+	}
+
+	// let's access an unexported field, which should give an error
+	f = s.Field("d")
+	err = f.Zero()
+	if err != errNotExported {
+		t.Error(err)
+	}
+
+	f = s.Field("Bar")
+	err = f.Zero()
+	if err != nil {
+		t.Error(err)
+	}
+
+	f = s.Field("E")
+	err = f.Zero()
+	if err != nil {
+		t.Error(err)
+	}
+
+	v := s.Field("E").value
+	if !v.IsNil() {
+		t.Errorf("could not set baz. Got: %s Want: <nil>", v.Interface())
+	}
+}
+
 func TestField(t *testing.T) {
 	s := newStruct()