ANTLR4 Version 4.5.4 CPP target: Compile problem with visitors

[Marcel Schaible]

Hi,

we are trying to use vistors with the new cpp runtime target. Our custom vistor class is defined like this:

class MyVisitor : public MyBaseVisitor<int>

Visual Studio 2015 produces the following error:

2>antlr-parser\runtime\src\tree\abstractparsetreevisitor.h(70): error C2664: 'bool antlr4::tree::AbstractParseTreeVisitor<T>::shouldVisitNextChild(antlr4::tree::RuleNode *,T)': cannot convert argument 2 from 'int *' to 'int'

2>                 with

2>                 [

2>                     T=int

2>                 ]

2>         antlr-parser\runtime\src\tree\abstractparsetreevisitor.h(70): note: There is no context in which this conversion is possible

2>         antlr-parser\runtime\src\tree\abstractparsetreevisitor.h(66): note: while compiling class template member function 'int *antlr4::tree::AbstractParseTreeVisitor<T>::visitChildren(antlr4::tree::RuleNode *)'

2>                 with

2>                 [

2>                     T=int

2>                 ]

2>         antlr-parser\demo\generated\tinypl90cbasevisitor.h(18): note: see reference to class template instantiation 'antlr4::tree::AbstractParseTreeVisitor<T>' being compiled

2>                 with

2>                 [

2>                     T=int

2>                 ]

2>         antlr-parser\demo\windows\antlr4-cpp-demo\main.cpp(31): note: see reference to class template instantiation 'MyBaseVisitor<int>' being compiled

2>

With the Java runtime I would define a visitor class like this:

public class MyOwnVisitor extends MyBaseVisitor<ST> implements MyVisitor<ST>

Can anyone give a short example how this is intended to work in C++?

Any idea or hint is appreciated ;-)

Thanks for your help

Marcel

[Mike Lischke]

Hey Marcel,

we trying to use vistors with the new cpp runtime target. Our custom vistor class is defined like this:

class ShipItWinnerVisitor : public TinyPL90CBaseVisitor<int>

Visual Studio 2015 produces the following error:

2>antlr-parser\runtime\src\tree\abstractparsetreevisitor.h(70): error C2664: 'bool antlr4::tree::AbstractParseTreeVisitor<T>::shouldVisitNextChild(antlr4::tree::RuleNode *,T)': cannot convert argument 2 from 'int *' to 'int'

2>                 with

2>                 [

2>                     T=int

2>                 ]

2>         antlr-parser\runtime\src\tree\abstractparsetreevisitor.h(70): note: There is no context in which this conversion is possible

2>         antlr-parser\runtime\src\tree\abstractparsetreevisitor.h(66): note: while compiling class template member function 'int *antlr4::tree::AbstractParseTreeVisitor<T>::visitChildren(antlr4::tree::RuleNode *)'

2>                 with

2>                 [

2>                     T=int

2>                 ]

2>         antlr-parser\demo\generated\tinypl90cbasevisitor.h(18): note: see reference to class template instantiation 'antlr4::tree::AbstractParseTreeVisitor<T>' being compiled

2>                 with

2>                 [

2>                     T=int

2>                 ]

2>         antlr-parser\demo\windows\antlr4-cpp-demo\main.cpp(31): note: see reference to class template instantiation 'TinyPL90CBaseVisitor<int>' being compiled

2>

I think there is a problem in the C++ runtime. Probably introduced by the automatic Java-to-C++ convertor and never been corrected. Anyway, in Java the ParseTreeVisitor class returns the same type in all visitor methods as it was parameterized to, while in C++ the return values are pointers to the parameterized type. I'll change this so that the ParseTreeVisitor class behaves the same in C++ (similar for the code generation).

Mike
-- 
www.soft-gems.net

[Mike Lischke]

I have now reworked the visitor handling in a way that doesn't require virtual template functions (which would be the natural translation of the Java generics code). Instead there is now a small Any class (similar like boost::any) which is used to return results from visits (hence no templates needed anymore for visitors). I checked that with a very simple test visitor for my MySQL grammar:

class TestParseVisitor : public MySQLParserBaseVisitor {

  virtual Any visitSelect_item(MySQLParser::Select_itemContext *context) override {

    Any result = visitChildren(context);

    std::cout << "Expression result: " << result.as<int>() << std::endl;

    return result;

  }

  virtual Any visitAdditive_expression(MySQLParser::Additive_expressionContext *context) override {

    Any result = visit(context->children[0].get());

    size_t i = 1;

    while (i < context->children.size()) {

      std::string op = context->children[i++]->getText();

      Any right = visit(context->children[i++].get());

      if (op == "+")

        result = result.as<int>() + right.as<int>();

      else

        result = result.as<int>() - right.as<int>();

    }

    return result;

  }

  virtual Any visitMultiplicative_expression(MySQLParser::Multiplicative_expressionContext *context) override {

    Any result = visit(context->children[0].get());

    size_t i = 1;

    while (i < context->children.size()) {

      std::string op = context->children[i++]->getText();

      Any right = visit(context->children[i++].get());

      switch (op[0]) {

        case '*':

          result = result.as<int>() * right.as<int>();

          break;

        case '/':

        case 'd': // DIV

        case 'D':

          result = result.as<int>() / right.as<int>();

          break;

        case '%':

        case 'm': // MOD

        case 'M':

          result = result.as<int>() % right.as<int>();

        break;

      }

    }

    return result;

  }

  virtual Any visitExpression_list_with_parentheses(MySQLParser::Expression_list_with_parenthesesContext *context) override {

    return visit(context->expression_list().get());

  }

  virtual Any visitLiteral(MySQLParser::LiteralContext *context) override

  {

    return std::atoi(context->start->getText().c_str());

  }

};

The ANLTR 4.5.4 snapshot jar as well as all other packages on my homepage (source code, prebuilt libraries) have been updated to include this and other recent changes.

Mike
-- 
www.soft-gems.net