Re: C++ PATCH for c++/91844 - Implement CWG 2352, Similar types and reference binding.

[Jason Merrill <jason at redhat dot com>]

On 9/22/19 3:23 PM, Marek Polacek wrote:
> +  /* Informally, two types are similar if, ignoring top-level cv-qualification:
> +     * they are the same type; or
> +     * they are both pointers, and the pointed-to types are similar; or
> +     * they are both pointers to member of the same class, and the types of
> +       the pointed-to members are similar; or
> +     * they are both arrays of the same size or both arrays of unknown bound,
> +       and the array element types are similar.  */

Yes.

> +  if ((TREE_CODE (type1) == POINTER_TYPE && TREE_CODE (type2) == POINTER_TYPE)
> +      || (TYPE_PTRDATAMEM_P (type1) && TYPE_PTRDATAMEM_P (type2))
> +      || (TREE_CODE (type1) == ARRAY_TYPE && TREE_CODE (type2) == ARRAY_TYPE))
> +    {
> +      int result = comp_cv_qual_signature (TREE_TYPE (type1),
> +					   TREE_TYPE (type2));

Using comp_cv_qual_signature means that we only return true if one 
cv-qualification signature is a subset of the other, but the definition 
of 'similar' is such that we should completely ignore cv-quals.  int 
const ** and int *const* are similar even though neither can convert to 
the other.

Jason