Move attribute set data structures into their own header file.

This modification moves Attr and Bindings structures into their own header
file which is dedicated to the attribute set representation. The goal of to
isolate pieces of code which are related to the attribute set
representation. Thus future modifications of the attribute set
representation will only have to modify these files, and not every other
file across the evaluator.

4 files changed, 142 insertions, 94 deletions

diff --git a/src/libexpr/attr-set.cc b/src/libexpr/attr-set.cc
new file mode 100644
index 000000000000..9ac5e603199a
--- /dev/null
+++ b/src/libexpr/attr-set.cc
@@ -0,0 +1,59 @@
+#include "attr-set.hh"
+#include "eval.hh"
+
+#include <algorithm>
+
+
+namespace nix {
+
+
+static void * allocBytes(size_t n)
+{
+    void * p;
+#if HAVE_BOEHMGC
+    p = GC_malloc(n);
+#else
+    p = malloc(n);
+#endif
+    if (!p) throw std::bad_alloc();
+    return p;
+}
+
+
+/* Allocate a new array of attributes for an attribute set with a specific
+   capacity. The space is implicitly reserved after the Bindings
+   structure. */
+Bindings * EvalState::allocBindings(Bindings::size_t capacity)
+{
+    return new (allocBytes(sizeof(Bindings) + sizeof(Attr) * capacity)) Bindings(capacity);
+}
+
+
+void EvalState::mkAttrs(Value & v, unsigned int expected)
+{
+    clearValue(v);
+    v.type = tAttrs;
+    v.attrs = allocBindings(expected);
+    nrAttrsets++;
+    nrAttrsInAttrsets += expected;
+}
+
+
+/* Create a new attribute named 'name' on an existing attribute set stored
+   in 'vAttrs' and return the newly allocated Value which is associated with
+   this attribute. */
+Value * EvalState::allocAttr(Value & vAttrs, const Symbol & name)
+{
+    Value * v = allocValue();
+    vAttrs.attrs->push_back(Attr(name, v));
+    return v;
+}
+
+
+void Bindings::sort()
+{
+    std::sort(begin(), end());
+}
+
+
+}
diff --git a/src/libexpr/attr-set.hh b/src/libexpr/attr-set.hh
new file mode 100644
index 000000000000..7cf6a9c58086
--- /dev/null
+++ b/src/libexpr/attr-set.hh
@@ -0,0 +1,82 @@
+#pragma once
+
+#include "nixexpr.hh"
+#include "symbol-table.hh"
+
+#include <algorithm>
+
+namespace nix {
+
+
+class EvalState;
+struct Value;
+
+/* Map one attribute name to its value. */
+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) { };
+    bool operator < (const Attr & a) const
+    {
+        return name < a.name;
+    }
+};
+
+/* Bindings contains all the attributes of an attribute set. It is defined
+   by its size and its capacity, the capacity being the number of Attr
+   elements allocated after this structure, while the size corresponds to
+   the number of elements already inserted in this structure. */
+class Bindings
+{
+public:
+    typedef uint32_t size_t;
+
+private:
+    size_t size_, capacity_;
+    Attr attrs[0];
+
+    Bindings(size_t capacity) : size_(0), capacity_(capacity) { }
+    Bindings(const Bindings & bindings) = delete;
+
+public:
+    size_t size() const { return size_; }
+
+    bool empty() const { return !size_; }
+
+    typedef Attr * iterator;
+
+    void push_back(const Attr & attr)
+    {
+        assert(size_ < capacity_);
+        attrs[size_++] = attr;
+    }
+
+    iterator find(const Symbol & name)
+    {
+        Attr key(name, 0);
+        iterator i = std::lower_bound(begin(), end(), key);
+        if (i != end() && i->name == name) return i;
+        return end();
+    }
+
+    iterator begin() { return &attrs[0]; }
+    iterator end() { return &attrs[size_]; }
+
+    Attr & operator[](size_t pos)
+    {
+        return attrs[pos];
+    }
+
+    void sort();
+
+    size_t capacity() { return capacity_; }
+
+    friend class EvalState;
+};
+
+
+}
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index d61ee7e80795..eab38c9da174 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -55,12 +55,6 @@ static void * allocBytes(size_t n)
 }
 
 
-void Bindings::sort()
-{
-    std::sort(begin(), end());
-}
-
-
 static void printValue(std::ostream & str, std::set<const Value *> & active, const Value & v)
 {
     if (active.find(&v) != active.end()) {
@@ -503,20 +497,6 @@ Env & EvalState::allocEnv(unsigned int size)
 }
 
 
-Value * EvalState::allocAttr(Value & vAttrs, const Symbol & name)
-{
-    Value * v = allocValue();
-    vAttrs.attrs->push_back(Attr(name, v));
-    return v;
-}
-
-
-Bindings * EvalState::allocBindings(Bindings::size_t capacity)
-{
-    return new (allocBytes(sizeof(Bindings) + sizeof(Attr) * capacity)) Bindings(capacity);
-}
-
-
 void EvalState::mkList(Value & v, unsigned int length)
 {
     clearValue(v);
@@ -527,16 +507,6 @@ void EvalState::mkList(Value & v, unsigned int length)
 }
 
 
-void EvalState::mkAttrs(Value & v, unsigned int expected)
-{
-    clearValue(v);
-    v.type = tAttrs;
-    v.attrs = allocBindings(expected);
-    nrAttrsets++;
-    nrAttrsInAttrsets += expected;
-}
-
-
 unsigned long nrThunks = 0;
 
 static inline void mkThunk(Value & v, Env & env, Expr * expr)
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 627fae3ff363..1b546f89c836 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -1,5 +1,6 @@
 #pragma once
 
+#include "attr-set.hh"
 #include "value.hh"
 #include "nixexpr.hh"
 #include "symbol-table.hh"
@@ -18,70 +19,6 @@ namespace nix {
 class EvalState;
 
 
-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) { };
-    bool operator < (const Attr & a) const
-    {
-        return name < a.name;
-    }
-};
-
-
-class Bindings
-{
-public:
-    typedef uint32_t size_t;
-
-private:
-    size_t size_, capacity_;
-    Attr attrs[0];
-
-    Bindings(size_t capacity) : size_(0), capacity_(capacity) { }
-    Bindings(const Bindings & bindings) = delete;
-
-public:
-    size_t size() const { return size_; }
-
-    bool empty() const { return !size_; }
-
-    typedef Attr * iterator;
-
-    void push_back(const Attr & attr)
-    {
-        assert(size_ < capacity_);
-        attrs[size_++] = attr;
-    }
-
-    iterator find(const Symbol & name)
-    {
-        Attr key(name, 0);
-        iterator i = std::lower_bound(begin(), end(), key);
-        if (i != end() && i->name == name) return i;
-        return end();
-    }
-
-    iterator begin() { return &attrs[0]; }
-    iterator end() { return &attrs[size_]; }
-
-    Attr & operator[](size_t pos)
-    {
-        return attrs[pos];
-    }
-
-    void sort();
-
-    size_t capacity() { return capacity_; }
-
-    friend class EvalState;
-};
-
-
 typedef void (* PrimOpFun) (EvalState & state, const Pos & pos, Value * * args, Value & v);