about summary refs log tree commit diff
path: root/src/libexpr/symbol-table.hh
diff options
context:
space:
mode:
authorEelco Dolstra <e.dolstra@tudelft.nl>2010-05-12T13·59+0000
committerEelco Dolstra <e.dolstra@tudelft.nl>2010-05-12T13·59+0000
commit8032f26ca0bd2233de066ce5786ff976bbd641ae (patch)
tree954b2ecdce037dcf47b0376616ac05dbad8542ab /src/libexpr/symbol-table.hh
parent4750065ada362bd46e85879975a3148e18df5b0c (diff)
parentbd25ac2260267abd2181324e1650820da70e5e60 (diff)
* Merged the `fast-eval' branch.
Diffstat (limited to 'src/libexpr/symbol-table.hh')
-rw-r--r--src/libexpr/symbol-table.hh81
1 files changed, 81 insertions, 0 deletions
diff --git a/src/libexpr/symbol-table.hh b/src/libexpr/symbol-table.hh
new file mode 100644
index 000000000000..424c2353899e
--- /dev/null
+++ b/src/libexpr/symbol-table.hh
@@ -0,0 +1,81 @@
+#ifndef __SYMBOL_TABLE_H
+#define __SYMBOL_TABLE_H
+
+#include <map>
+#include <tr1/unordered_set>
+
+#include "types.hh"
+
+namespace nix {
+
+/* Symbol table used by the parser and evaluator to represent and look
+   up identifiers and attribute sets 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:
+    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 empty() const
+    {
+        return s->empty();
+    }
+
+    friend std::ostream & operator << (std::ostream & str, const Symbol & sym);
+};
+
+inline std::ostream & operator << (std::ostream & str, const Symbol & sym)
+{
+    str << *sym.s;
+    return str;
+}
+
+class SymbolTable
+{
+private:
+    typedef std::tr1::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);
+    }
+
+    unsigned int size() const
+    {
+        return symbols.size();
+    }
+};
+
+}
+
+#endif /* !__SYMBOL_TABLE_H */