Re: How to adapt an AST involving forward declared meta data

On Fri, Nov 2, 2018 at 11:30 AM Larry Evans <[email protected]> wrote:
>
> On 11/1/18 9:05 AM, Michael Powell wrote:
> > On Wed, Oct 31, 2018 at 10:15 PM Michael Powell <[email protected]> wrote:
> >>
> >> Hello,
> >>
> >> Like the subject says, I've got some structs in my AST that have to be
> >> forward declared.

I'll consider that simplification, thanks for that suggestion.

The chief block I am having right now is the forward declaration,
however. I think whether I am specializing a template class versus the
concrete class, I'm going to run into a forward declaration one way or
another.

> > Okay, I've worked through the basic AST concepts I think I need for
> > this problem. However, the VS2017 C2079 error is not going away, not
> > without modifying the approach:
> >
> > One possible way is to "introduce" pointers into the AST. Question
> > along these lines, how good is Spirit Qi at working with AST,
> > pointers, etc? Smart pointers preferred, I think, if possible.
> >
> > struct bool_t {
> >      std::string val;
> > };
> >
> > struct str_t {
> >      std::string quoted_text;
> > };
> >
> > struct full_id_t {
> >      std::string full_id;
> > };
> >
> > struct int_t {
> >      std::string val;
> > };
> >
> > struct float_t {
> >      std::string val;
> > };
> >
> IIRC, one problem with boost::variant and possible spirit::variant is
> the ambiguity when types or duplicated.  IOW:
>
>    variant<T,T,T> v3t;
>
> doesn't work because assignment:
>
>    v3t = T{};
>
> doesn't know which of the 3 T's is meant.  T, in your case, is
> std::string.  You've solved it by essentially repeated the
> same value type (i.e. std::string) wrapped in a different class.
>
> A possible simplification is:
>
> enum types
> { bool_t
> , str_t
> , full_id_t
> , int_t
> , float_t
> };
>
> template<types Type>
> struct value_t
> { std::string value_v
> };
>
> It would save a little typing.
>
> -regards,
> Larry
>
>
>
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