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refactor(3p/nix/libexpr): Use absl::node_hash_set in SymbolTable

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This replaces the previous use of std::unordered_set with
absl::node_hash_set.

This type was chosen because the current implementation requires
pointer stability.

This does not yet touch the 'Attr' struct.

As a bonus, the implementation of the SymbolTable struct is now
consolidated into a single header/implementation file pair.
This commit is contained in:
Vincent Ambo 2020-05-21 04:53:09 +01:00
parent 00017ace04
commit 97e85f94e5
3 changed files with 39 additions and 32 deletions
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37
third_party/nix/src/libexpr/symbol-table.hh vendored
View file

@ -1,11 +1,11 @@
#pragma once
#include <map>
#include <unordered_set>
#include <absl/container/node_hash_set.h>
#include <absl/strings/string_view.h>
#include "types.hh"
namespace nix {
namespace nix { // TODO(tazjin): ::expr
/* Symbol table used by the parser and evaluator to represent and look
up identifiers and attributes efficiently. SymbolTable::create()
@ -15,8 +15,8 @@ namespace nix {
class Symbol {
private:
const string* s; // pointer into SymbolTable
Symbol(const string* s) : s(s){};
const std::string* s; // pointer into SymbolTable
Symbol(const std::string* s) : s(s){};
friend class SymbolTable;
public:
@ -28,7 +28,7 @@ class Symbol {
bool operator<(const Symbol& s2) const { return s < s2.s; }
operator const string&() const { return *s; }
operator const std::string&() const { return *s; }
bool set() const { return s; }
@ -38,26 +38,19 @@ class Symbol {
};
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);
}
Symbol Create(absl::string_view sym);
size_t size() const { return symbols.size(); }
// TODO(tazjin): two of these?
size_t Size() const;
size_t totalSize() const;
// Return the total size (in bytes)
size_t TotalSize() const;
template <typename T>
void dump(T callback) {
for (auto& s : symbols) {
callback(s);
}
}
private:
// flat_hash_set does not retain pointer stability on rehashing,
// hence "interned" strings/symbols are stored on the heap.
absl::node_hash_set<std::string> symbols_;
};
} // namespace nix