Re: Union Type Object problem

[Laurence Finston]

Unions can't contain objects with constructors. 
This has come up recently, so if you look in the archives you can find
references to Stroustrup and the standard, if you're interested.

Laurence

-------------------
> Hi,
> I have to do a parser in Bison and I need to use in %union{} construct
> some type Object.
> I have this example-class Expression:
> 
> class Expression {
> public:
>    virtual ~Expression () {}
>    //  It's necessary because we need to clone objects without
>    // knowing the exact type.
>    virtual Expression *clone () = 0;
>    // The value represented by the expression
>    virtual int value () = 0;
> };
> 
> this is a very simple class, but when I define the Bison Type in
> union construct in this way:
> 
> %union{
>    Expression *exp;
>    int num;
> }
> 
> the compiler give me this error:
> 
> >> error: syntax error before `*' token
> 
> I compile this file Bison like this:
> bash> bison -d parser.y 
> bash> flex     parser.lex
> bash> g++  -DCPLUSPLUS parser.tab.c lex.yy.c -lfl -o parser
> 
> Thanks a lot.
> Enrico
> 
> 
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