symbol-table.hh

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#pragma once
 
#include <unordered_map>
 
#include "lix/libutil/types.hh"
#include "lix/libutil/chunked-vector.hh"
 
namespace nix {

class SymbolStr
{
    friend class SymbolTable;
 
private:
    const std::string * s;
 
    explicit SymbolStr(const std::string & symbol): s(&symbol) {}
 
public:
    bool operator == (std::string_view s2) const
    {
        return *s == s2;
    }
 
    operator const std::string & () const
    {
        return *s;
    }
 
    operator const std::string_view () const
    {
        return *s;
    }
 
    friend std::ostream & operator <<(std::ostream & os, const SymbolStr & symbol);
};

class Symbol
{
    friend class SymbolTable;
 
private:
    uint32_t id;
 
    explicit Symbol(uint32_t id): id(id) {}
 
public:
    Symbol() : id(0) {}
 
    explicit operator bool() const { return id > 0; }
 
    bool operator<(const Symbol other) const { return id < other.id; }
    bool operator==(const Symbol other) const { return id == other.id; }
    bool operator!=(const Symbol other) const { return id != other.id; }
};

class SymbolTable
{
private:
    std::unordered_map<std::string_view, std::pair<const std::string *, uint32_t>> symbols;
    ChunkedVector<std::string, 8192> store{16};
 
public:

    Symbol create(std::string_view s)
    {
        // Most symbols are looked up more than once, so we trade off insertion performance
        // for lookup performance.
        // TODO: could probably be done more efficiently with transparent Hash and Equals
        // on the original implementation using unordered_set
        // FIXME: make this thread-safe.
        auto it = symbols.find(s);
        if (it != symbols.end()) return Symbol(it->second.second + 1);
 
        const auto & [rawSym, idx] = store.add(std::string(s));
        symbols.emplace(rawSym, std::make_pair(&rawSym, idx));
        return Symbol(idx + 1);
    }
 
    SymbolStr operator[](Symbol s) const
    {
        if (s.id == 0 || s.id > store.size())
            abort();
        return SymbolStr(store[s.id - 1]);
    }
 
    size_t size() const
    {
        return store.size();
    }
 
    size_t totalSize() const;
 
    template<typename T>
    void dump(T callback) const
    {
        store.forEach(callback);
    }
};
 
}