extends CompositeWithSubfields to make the interface check no the specific type

Author: Stashchenko

field/composite.go

@@ -17,10 +17,23 @@ import (
 	"github.com/moov-io/iso8583/utils"
 )
 
+// CompositeWithSubfields provides methods to manipulate subfields
+// and used when composite field is created without
+// calling NewComposite e.g. in iso8583.NewMessage(...)
+type CompositeWithSubfields interface {
+	ConstructSubfields()
+	GetSubfields() map[string]Field
+	SetSubfields(idPath string, value string) error
+	SetSubfield(id string, value string) error
+	UnsetSubfields(idPaths ...string) error
+	UnsetSubfield(id string)
+}
+
 var (
-	_ Field            = (*Composite)(nil)
-	_ json.Marshaler   = (*Composite)(nil)
-	_ json.Unmarshaler = (*Composite)(nil)
+	_ Field                  = (*Composite)(nil)
+	_ json.Marshaler         = (*Composite)(nil)
+	_ json.Unmarshaler       = (*Composite)(nil)
+	_ CompositeWithSubfields = (*Composite)(nil)
 )
 
 // Composite is a wrapper object designed to hold ISO8583 TLVs, subfields and
@@ -93,12 +106,6 @@ func NewComposite(spec *Spec) *Composite {
 	return f
 }
 
-// CompositeWithSubfields is used when composite field is created without
-// calling NewComposite e.g. in iso8583.NewMessage(...)
-type CompositeWithSubfields interface {
-	ConstructSubfields()
-}
-
 // ConstructSubfields creates subfields according to the spec
 // this method is used when composite field is created without
 // calling NewComposite (when we create message spec and composite spec)
@@ -732,7 +739,7 @@ func (m *Composite) UnsetSubfields(idPaths ...string) error {
 				return fmt.Errorf("subfield %s does not exist", id)
 			}
 
-			composite, ok := f.(*Composite)
+			composite, ok := f.(CompositeWithSubfields)
 			if !ok {
 				return fmt.Errorf("field %s is not a composite field and its subfields %s cannot be unset", id, path)
 			}
@@ -767,7 +774,7 @@ func (m *Composite) SetSubfields(idPath string, value string) error {
 	}
 
 	// If there's a further path, the subfield must be a composite
-	composite, ok := subfield.(*Composite)
+	composite, ok := subfield.(CompositeWithSubfields)
 	if !ok {
 		return fmt.Errorf("subfield %s is not a composite field and cannot have nested subfields", id)
 	}

message.go

@@ -631,7 +631,7 @@ func (m *Message) UnsetFields(idPaths ...string) error {
 				return fmt.Errorf("field %d does not exist", idx)
 			}
 
-			composite, ok := f.(*field.Composite)
+			composite, ok := f.(field.CompositeWithSubfields)
 			if !ok {
 				return fmt.Errorf("field %d is not a composite field and its subfields %s cannot be unset", idx, path)
 			}
@@ -680,7 +680,7 @@ func (m *Message) SetField(path string, val string) error {
 	}
 
 	// If there's a subpath, the field must be a composite
-	composite, ok := f.(*field.Composite)
+	composite, ok := f.(field.CompositeWithSubfields)
 	if !ok {
 		return fmt.Errorf("field %d is not a composite field and cannot have subfields", fieldID)
 	}