* Store attribute sets as a vector instead of a map (i.e. a red-black

  tree).  This saves a lot of memory.  The vector should be sorted so
  that names can be looked up using binary search, but this is not the
  case yet.  (Surprisingly, looking up attributes using linear search
  doesn't have a big impact on performance.)

  Memory consumption for

    $ nix-instantiate /etc/nixos/nixos/tests -A bittorrent.test --readonly-mode

  on x86_64-linux with GC enabled is now 185 MiB (compared to 946
  MiB on the trunk).

1 files changed, 16 insertions, 2 deletions

diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index ec4939442515..2f1b3fa4595e 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -20,13 +20,24 @@ struct Env;
 struct Value;
 struct Attr;
 
+
+/* Attribute sets are represented as a vector of attributes, sorted by
+   symbol (i.e. pointer to the attribute name in the symbol table). */
 #if HAVE_BOEHMGC
-typedef std::map<Symbol, Attr, std::less<Symbol>, gc_allocator<std::pair<const Symbol, Attr> > > Bindings;
+typedef std::vector<Attr, gc_allocator<Attr> > BindingsBase;
 #else
-typedef std::map<Symbol, Attr> Bindings;
+typedef std::vector<Attr> BindingsBase;
 #endif
 
 
+class Bindings : public BindingsBase
+{
+public:
+    iterator find(const Symbol & name);
+    Attr & operator [] (const Symbol & name);
+};
+
+
 typedef enum {
     tInt = 1,
     tBool,
@@ -125,8 +136,11 @@ struct Env
 
 struct Attr
 {
+    Symbol name;
     Value * value;
     Pos * pos;
+    Attr(Symbol name, Value * value, Pos * pos = &noPos)
+        : name(name), value(value), pos(pos) { };
     Attr() : pos(&noPos) { };
 };