Re: Help understanding overloaded templates

["Doug Gregor" <doug dot gregor at gmail dot com>]

On 11/15/07, Rob Quill <rob.quill@gmail.com> wrote:
> Hi,
>
> I was wondering if anyone could help me make sense of the
> more_specialized_fn() function in pt.c (line 13281).
>
> Specifically, I am trying to understand what each of the are:
>
>   tree decl1 = DECL_TEMPLATE_RESULT (pat1);

This is the actual FUNCTION_DECL node that represents the function
template. It's just like another other (non-template) FUNCTION_DECL,
except that it's associated with a template and will use some of the
template parameters in its definition and declaration.

>   tree targs1 = make_tree_vec (DECL_NTPARMS (pat1));

DECL_NTPARMS is the number of template parameters, so we're just
making a vector that long.

>   tree tparms1 = DECL_INNERMOST_TEMPLATE_PARMS (pat1);

For member templates, this pulls out just the innermost template parameters.

>   tree args1 = TYPE_ARG_TYPES (TREE_TYPE (decl1));

This is the list of function parameter types. e.g., in a function template

  template<typename T>
  void f(T*, int, float);

this would be a TREE_LIST containing the types T*,, int, and float.

> and how the function is supposed to deal with variadic functions in
> terms of these. That is to say, if a function is variadic, how is that
> represented in these data structures?

By "variadic" I assume you mean C-style variadic functions, e.g.,

  template<typename T> void f(T x, ...);

and not the C++0x variadic templates.

The presence of an ellipsis is indicated by the last node in the
TREE_LIST being void_list_node; if there is no ellipsis, the last
parameter's TREE_CHAIN will simply be NULL_TREE.

  - Doug