Add support for identityref data type

Change-Id: I369150b83d86a4c22fadf383ee011eee619a4c15
diff --git a/src/ast_commands.cpp b/src/ast_commands.cpp
index 55b6ccd..a4a9e08 100644
--- a/src/ast_commands.cpp
+++ b/src/ast_commands.cpp
@@ -14,6 +14,19 @@
 {
 }
 
+identityRef_::identityRef_() = default;
+
+identityRef_::identityRef_(const std::string& value)
+    : m_value(value)
+{
+}
+
+identityRef_::identityRef_(const std::string& module, const std::string& value)
+    : m_prefix(module_{module})
+    , m_value(value)
+{
+}
+
 binary_::binary_() = default;
 
 binary_::binary_(const std::string& value)
@@ -36,6 +49,11 @@
     return this->m_path == b.m_path && this->m_options == b.m_options;
 }
 
+bool identityRef_::operator==(const identityRef_& b) const
+{
+    return this->m_prefix == b.m_prefix && this->m_value == b.m_value;
+}
+
 bool binary_::operator==(const binary_& b) const
 {
     return this->m_value == b.m_value;