1 files changed, 51 insertions, 0 deletions
diff --git a/var-value.go b/var-value.go
new file mode 100644
index 0000000..ff97104
--- /dev/null
+++ b/var-value.go
@@ -0,0 +1,51 @@
+package stm
+
+type VarValue interface {
+	Set(interface{}) VarValue
+	Get() interface{}
+	Changed(VarValue) bool
+}
+
+type version uint64
+
+type versionedValue struct {
+	value   interface{}
+	version version
+}
+
+func (me versionedValue) Set(newValue interface{}) VarValue {
+	return versionedValue{
+		value:   newValue,
+		version: me.version + 1,
+	}
+}
+
+func (me versionedValue) Get() interface{} {
+	return me.value
+}
+
+func (me versionedValue) Changed(other VarValue) bool {
+	return me.version != other.(versionedValue).version
+}
+
+type customVarValue struct {
+	value   interface{}
+	changed func(interface{}, interface{}) bool
+}
+
+var _ VarValue = customVarValue{}
+
+func (me customVarValue) Changed(other VarValue) bool {
+	return me.changed(me.value, other.(customVarValue).value)
+}
+
+func (me customVarValue) Set(newValue interface{}) VarValue {
+	return customVarValue{
+		value:   newValue,
+		changed: me.changed,
+	}
+}
+
+func (me customVarValue) Get() interface{} {
+	return me.value
+}