1 files changed, 87 insertions, 0 deletions
diff --git a/third_party/nix/src/libexpr/symbol-table.hh b/third_party/nix/src/libexpr/symbol-table.hh
new file mode 100644
index 000000000000..91faea122ce1
--- /dev/null
+++ b/third_party/nix/src/libexpr/symbol-table.hh
@@ -0,0 +1,87 @@
+#pragma once
+
+#include <map>
+#include <unordered_set>
+
+#include "types.hh"
+
+namespace nix {
+
+/* Symbol table used by the parser and evaluator to represent and look
+   up identifiers and attributes efficiently.  SymbolTable::create()
+   converts a string into a symbol.  Symbols have the property that
+   they can be compared efficiently (using a pointer equality test),
+   because the symbol table stores only one copy of each string. */
+
+class Symbol
+{
+private:
+    const string * s; // pointer into SymbolTable
+    Symbol(const string * s) : s(s) { };
+    friend class SymbolTable;
+
+public:
+    Symbol() : s(0) { };
+
+    bool operator == (const Symbol & s2) const
+    {
+        return s == s2.s;
+    }
+
+    bool operator != (const Symbol & s2) const
+    {
+        return s != s2.s;
+    }
+
+    bool operator < (const Symbol & s2) const
+    {
+        return s < s2.s;
+    }
+
+    operator const string & () const
+    {
+        return *s;
+    }
+
+    bool set() const
+    {
+        return s;
+    }
+
+    bool empty() const
+    {
+        return s->empty();
+    }
+
+    friend std::ostream & operator << (std::ostream & str, const Symbol & sym);
+};
+
+class SymbolTable
+{
+private:
+    typedef std::unordered_set<string> Symbols;
+    Symbols symbols;
+
+public:
+    Symbol create(const string & s)
+    {
+        std::pair<Symbols::iterator, bool> res = symbols.insert(s);
+        return Symbol(&*res.first);
+    }
+
+    size_t size() const
+    {
+        return symbols.size();
+    }
+
+    size_t totalSize() const;
+
+    template<typename T>
+    void dump(T callback)
+    {
+        for (auto & s : symbols)
+            callback(s);
+    }
+};
+
+}