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POImplementing a symbol table for a compiler in C++
 

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  1. POImplementing a symbol table for a compiler in C++
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    <p>I am currently developing a small compiler for a language for problem definitions. You can imagine a bastard child of Lisp and Prolog. Now, to the case:</p> <p><a href="https://en.wikipedia.org/wiki/Functor" rel="nofollow">Functor</a> is a base class from which 3 classes inherit: A,B,C.</p> <p>I made a lexer and parser with ANTLR3C, which gives me an AST tree. I traverse the tree and when I find a function of type A, I create an object of type A with the data from the tree, and a sym_register object to hold it:</p> <pre class="lang-c prettyprint-override"><code>#ifndef SYM_REGISTER_H #define SYM_REGISTER_H #include &lt;vector&gt; #include &lt;string&gt; enum class Symbol_type : int { T_A, T_B, T_C, T_D }; class sym_register { public: std::string name; Symbol_type type; std::shared_ptr&lt;Functor&gt; declaration; std::vector &lt; InstancedFunctor &gt; result; sym_register(std::string n, Symbol_type t, std::shared_ptr&lt;Functor&gt; p){ name = n; type = t; declaration = p; } }; #endif </code></pre> <p>The Symbol_type enum class gives me the info of what kind of object is std::shared_ptr declaration; pointing to, so I should be able to retrieve the full information of the object. </p> <p>This is how I store the symbols in my main Problem class:</p> <pre class="lang-c prettyprint-override"><code>class Problem { std::map&lt; std::string, std::shared_ptr&lt;sym_register&gt; &gt; sym_table; }; </code></pre> <p>My problem is when I try to retrieve the symbols from the table, as I am not able to get the "declaration" attribute to its original class, I've tried using static_cast and reinterpret_cast with no results.</p> <p>So, here I have various questions:</p> <ol> <li>Is the "extra" information from the inherited classes lost when I store a pointer to an object of type A on a std::shared_ptr ?</li> <li>Should I go for a switch and an (unsafe) explicit conversion?</li> <li>Should I store pointers to NULL (a-la C) instead of std::shared_ptr ?</li> <li>What is the correct way to do it?</li> </ol> <p>EDIT: I basically want to be able to do:</p> <pre class="lang-c prettyprint-override"><code>std::shared_ptr&lt;A&gt; foo = Problem.getSymbol("objectWithTypeA"); // and so on with the rest of the class hierarchy ... </code></pre> <p>EDIT2: The compilation errors are:</p> <pre><code>std::shared_ptr&lt;A&gt; foo = it.second-&gt;declaration; // error: conversion from ‘std::shared_ptr&lt;Functor&gt;’ // to non-scalar type ‘std::shared_ptr&lt;A&gt;’ requested std::shared_ptr&lt;A&gt; foo(reinterpret_cast&lt;std::shared_ptr&lt;A&gt; &gt;(it.second-&gt;declaration)); // error: invalid cast from type ‘std::shared_ptr&lt;Functor&gt;’ // to type ‘std::shared_ptr&lt;A&gt;’ std::shared_ptr&lt;A&gt; foo(static_cast&lt;std::shared_ptr&lt;A&gt; &gt;(it.second-&gt;declaration)); // error: no matching function for call to ‘std::shared_ptr&lt;A&gt;::shared_ptr(std::shared_ptr&lt;Functor&gt;&amp;)’ // note: candidates are: // long list of template instantiations with a final // note: no known conversion for argument 1 // from ‘std::shared_ptr&lt;Functor&gt;’ to ‘const std::shared_ptr&lt;A&gt;&amp;’ std::shared_ptr&lt;A&gt; foo(static_cast&lt;A*&gt;(it.second-&gt;declaration)); // error: invalid static_cast from type ‘std::shared_ptr&lt;Functor&gt;’ to type ‘A*’ std::shared_ptr&lt;A&gt; foo(reinterpret_cast&lt;A*&gt;(it.second-&gt;declaration)); // error: invalid cast from type ‘std::shared_ptr&lt;Functor&gt;’ to type ‘A*’ </code></pre>
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    1. COWhat do you mean with not being able to get the "declaration" attribute? Is there a compilation error or a runtime error?
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    2. COBasically compilation errors, when I try to cast the "declaration" attribute to its original class (stored in the "type" attribute.
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      1. POImplementing a symbol table for a compiler in C++
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    3. COAnd what is the compilation error?
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