d470ec0d29
Replaces the previous uses of the (ordered!) std::map and std::set
with absl::flat_hash_{map|set}.
After some careful reading it seems that there is actually no
ordering dependency on these types, and the (drop-in) replacements
perform slightly better.
Overall this is not fixing a bottleneck, just a driveby thing.
Change-Id: Ided695dc75676bd58515aa9382df0be0a09c565e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1220
Reviewed-by: glittershark <grfn@gws.fyi>
Reviewed-by: isomer <isomer@tvl.fyi>
Tested-by: BuildkiteCI
69 lines
2 KiB
C++
69 lines
2 KiB
C++
#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
|