Re: Using C++ in GCC is OK

[Paolo Bonzini <bonzini at gnu dot org>]

On 06/01/2010 04:11 PM, Ian Lance Taylor wrote:
 In the gccgo IR I don't represent everything with a single type.
> Instead, I use a separate base class for types, expressions and
> statements (in Go there is more of a distinction between expressions
> and statements than there is in C/C++).  I represent specific types,
> etc., as child classes.  The base class uses a protected virtual
> function interface which the child classes implement.
>
> However, as you observe, some code does need to use pattern matching,
> so that approach is awkward to use by itself.  I also declare an enum
> in the base class, and so given a pointer to the base class you can
> examine that enum to know which kind of object you have.

This made me wondering if we are looking at the C++ conversion from the 
wrong point of view.

In particular, I wonder if the best use of C++ wouldn't be a set of 
functions (including templates, etc.) implementing a kind of RTTI with a 
less verbose syntax than what we have now.

Just to give an idea:

   template<enum tree_code CODE>
   static inline bool isa(tree t)
   {
     return TREE_CODE (t) == CODE;
   }

   template<enum tree_node_structure_enum TS>
   static inline bool isa(tree t)
   {
     return CODE_CONTAINS_STRUCT (TREE_CODE (t), TS);
   }

   template<enum tree_code_class CLASS>
   static inline bool isa(tree t)
   {
     return TREE_CODE_CLASS (TREE_CODE (t)) == CLASS;
   }

   template<enum rtx_code CODE>
   static inline bool isa(rtx t)
   {
     return GET_RTX_CODE (t) == CODE;
   }

This is just a stupid example of course, but my point is: are we sure 
that the main benefit of C++ comes from object-orientation?

Paolo