Is it possible to expand typedef with forced compiler error?

Question

I have been using method shown below to force compiler to yell at me a variable type:

template <class T>
struct show_type;

Using it with desired variable so compiler errors an incomplete struct type:

typedef int32_t s32;
s32 a;
show_type<decltype(a)>();

So GCC 5.3.0 produces error:

invalid use of incomplete type 'struct show_type<int>'

And MSVC 2015:

'show_type<s32>': no appropriate default constructor available

Now I wonder if there is a way to force an error to show full hierarchy of typedefs (that is, s32 -> int32_t -> int), or at least newest typedef and first original type? I don't mind dirty or evil tricks.

Answer 1

Now I wonder if there is a way to force an error to show full hierarchy of typedefs (that is, s32 -> int32_t -> int), or at least newest typedef and first original type?

There is no such hierarchy. s32 is int32_t is int. There is no way to differentiate those three types, since they aren't actually three different types. Two of those are just aliases.

---

What you're really looking for is static reflection, or P0194. That would allow you to do something like:

using meta_s32   = reflexpr(s32);
using meta_int32 = meta::get_aliased_t<meta_s32>;
using meta_int   = meta::get_aliased_t<meta_int32>;
std::cout << meta::get_name_v<meta_s32> << ", "
          << meta::get_name_v<meta_int32> << ", "
          << meta::get_name_v<meta_int> << '\n';

You could produce the reflection hierarchy by repeatedly going up with get_aliased_t and stopping when is_alias_v yields false_type.