blob: c2599658859fa094f0c16455f7b2e7f5f116a5a2 (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
|
#pragma once
#include <absl/container/node_hash_set.h>
#include <absl/strings/string_view.h>
namespace nix { // TODO(tazjin): ::expr
// TODO(tazjin): Replace with a simpler struct, or get rid of.
class Symbol {
private:
const std::string* s; // pointer into SymbolTable
Symbol(const std::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 std::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);
template <typename H>
friend H AbslHashValue(H h, const Symbol& c) {
return H::combine(std::move(h), c.s);
}
};
// SymbolTable is a hash-set based symbol-interning mechanism.
//
// TODO(tazjin): Figure out which things use this. AttrSets, ...?
// Is it possible this only exists because AttrSet wasn't a map?
//
// Original comment:
//
// 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 SymbolTable {
public:
// Create a new symbol in this table by emplacing the provided
// string into it.
//
// The symbol will reference an existing symbol if the symbol is
// already interned.
Symbol Create(absl::string_view sym);
// Return the number of symbols interned.
size_t Size() const;
// Return the total size (in bytes)
size_t TotalSize() const;
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
|
