1 files changed, 68 insertions, 0 deletions
diff --git a/src/libutil/reference-set.hh b/src/libutil/reference-set.hh
new file mode 100644
index 000000000..ac4a9994e
--- /dev/null
+++ b/src/libutil/reference-set.hh
@@ -0,0 +1,68 @@
+#pragma once
+
+#include "comparator.hh"
+
+#include <set>
+
+namespace nix {
+
+template<typename Ref>
+struct References
+{
+    std::set<Ref> others;
+    bool self = false;
+
+    bool empty() const;
+    size_t size() const;
+
+    /* Functions to view references + self as one set, mainly for
+       compatibility's sake. */
+    std::set<Ref> possiblyToSelf(const Ref & self) const;
+    void insertPossiblyToSelf(const Ref & self, Ref && ref);
+    void setPossiblyToSelf(const Ref & self, std::set<Ref> && refs);
+
+    GENERATE_CMP(References<Ref>, me->others, me->self);
+};
+
+template<typename Ref>
+bool References<Ref>::empty() const
+{
+    return !self && others.empty();
+}
+
+template<typename Ref>
+size_t References<Ref>::size() const
+{
+    return (self ? 1 : 0) + others.size();
+}
+
+template<typename Ref>
+std::set<Ref> References<Ref>::possiblyToSelf(const Ref & selfRef) const
+{
+    std::set<Ref> refs { others };
+    if (self)
+        refs.insert(selfRef);
+    return refs;
+}
+
+template<typename Ref>
+void References<Ref>::insertPossiblyToSelf(const Ref & selfRef, Ref && ref)
+{
+    if (ref == selfRef)
+        self = true;
+    else
+        others.insert(std::move(ref));
+}
+
+template<typename Ref>
+void References<Ref>::setPossiblyToSelf(const Ref & selfRef, std::set<Ref> && refs)
+{
+    if (refs.count(selfRef)) {
+        self = true;
+        refs.erase(selfRef);
+    }
+
+    others = refs;
+}
+
+}