forked from lix-project/lix
ff0fd91ed2
the only use of this function is to determine whether a lambda has a non-set formal, but this use is arguably better served by Symbol::set and using a non-Symbol instead of an empty symbol in the parser when no such formal is present.
102 lines
2.1 KiB
C++
102 lines
2.1 KiB
C++
#pragma once
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#include <list>
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#include <map>
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#include <unordered_map>
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#include "types.hh"
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namespace nix {
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/* Symbol table used by the parser and evaluator to represent and look
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up identifiers and attributes efficiently. SymbolTable::create()
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converts a string into a symbol. Symbols have the property that
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they can be compared efficiently (using a pointer equality test),
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because the symbol table stores only one copy of each string. */
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class Symbol
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{
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private:
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const std::string * s; // pointer into SymbolTable
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Symbol(const std::string * s) : s(s) { };
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friend class SymbolTable;
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public:
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Symbol() : s(0) { };
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bool operator == (const Symbol & s2) const
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{
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return s == s2.s;
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}
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// FIXME: remove
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bool operator == (std::string_view s2) const
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{
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return s->compare(s2) == 0;
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}
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bool operator != (const Symbol & s2) const
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{
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return s != s2.s;
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}
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bool operator < (const Symbol & s2) const
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{
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return s < s2.s;
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}
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operator const std::string & () const
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{
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return *s;
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}
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operator const std::string_view () const
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{
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return *s;
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}
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bool set() const
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{
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return s;
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}
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friend std::ostream & operator << (std::ostream & str, const Symbol & sym);
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};
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class SymbolTable
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{
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private:
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std::unordered_map<std::string_view, Symbol> symbols;
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std::list<std::string> store;
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public:
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Symbol create(std::string_view s)
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{
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// Most symbols are looked up more than once, so we trade off insertion performance
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// for lookup performance.
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// TODO: could probably be done more efficiently with transparent Hash and Equals
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// on the original implementation using unordered_set
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auto it = symbols.find(s);
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if (it != symbols.end()) return it->second;
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auto & rawSym = store.emplace_back(s);
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return symbols.emplace(rawSym, Symbol(&rawSym)).first->second;
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}
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size_t size() const
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{
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return symbols.size();
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}
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size_t totalSize() const;
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template<typename T>
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void dump(T callback)
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{
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for (auto & s : store)
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callback(s);
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}
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};
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}
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