83 lines
2.8 KiB
C++
83 lines
2.8 KiB
C++
/*
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SYMBOL-TABLE.hpp - registry for automatically interned symbol string tokens
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Copyright (C)
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2017, Hermann Vosseler <Ichthyostega@web.de>
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**Lumiera** is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 2 of the License, or (at your
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option) any later version. See the file COPYING for further details.
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*/
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/** @file symbol-table.hpp
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** Registry table for automatically _interned strings_.
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** The implementation of the lib::Symbol token relies on unique string pointers,
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** such as to create one distinct identity for each distinct "symbol string". The idea
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** is to generate unique and distinct numeric token IDs, while still holding onto a human readable
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** string. Which in turn requires us to manage a registry of already known symbol strings; when a
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** Symbol object with such an already known string is created, it will thus connect internally
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** to the known token ID.
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**
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** @todo as of this writing (4/2017), it is neither clear if we really need such a facility, nor
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** do we know enough to judge the implementation approach taken here. It might well turn out
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** that a mere hash over the symbol string would be sufficient. Just the general vision for
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** Lumiera indicates that we're going to rely heavily on some kind of symbolic or meta processing,
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** involving a rules based query system, and in the light of such future developments, introducing
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** a distinct lib::Symbol datatype seemed like a good idea. When we started to generate command IDs
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** systematically, just literal c-string constants weren't sufficient anymore, leading to this
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** very preliminary table based implementation.
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**
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** @see symbol-impl.cpp
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** @see Symbol_test
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** @see Symbol_HashtableTest
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** @see SessionCommandFunction_test multithreaded access
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*/
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#ifndef LIB_SYMBOL_TABLE_H
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#define LIB_SYMBOL_TABLE_H
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#include "lib/sync.hpp"
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#include "lib/symbol.hpp"
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#include "lib/nocopy.hpp"
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#include <unordered_set>
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#include <utility>
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#include <string>
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namespace lib {
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using std::string;
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using std::move;
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/**
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* Table for automatically _interned strings_.
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* This table is used to back the lib::Symbol token type,
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* which is implemented by a pointer into this registration table
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* for each new distinct "symbol string" created.
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* @warning grows eternally, never shrinks
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*/
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class SymbolTable
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: public Sync<>
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, util::NonCopyable
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{
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std::unordered_set<string> table_;
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public:
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Literal
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internedString (string && symbolString)
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{
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Lock sync{this};
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auto res = table_.insert (move (symbolString));
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return res.first->c_str();
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}
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};
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} // namespace lib
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#endif /*LIB_SYMBOL_TABLE_H*/
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