const/non-const template type deduction with fused types

[evgeny.b...@gmail.com]

Hi,

I looking at this fused types / c++ template dediction issue, 

https://github.com/cython/cython/issues/6294

Poking around, it looks like template deduction code treats const and non-const types (e.g.  `const int32_t *` and `int32_t *`) as totally unrelated. Dropping a breakpoint, I see things like

```

(Pdb) arg_types_for_deduction[1]
<CPtrType <CConstOrVolatileType const <CTypedefType int32_t>>>
(Pdb) arg_types_for_deduction[1].typeof_name()
'const int32_t *'

```

So I wonder if there's  a recommended way to effectively const-cast, to construct from `arg_types_for_deduction[1]` above its non-const analog? My thought was that if there's a way, the template resolver can try const and non-const versions (around https://github.com/cython/cython/blob/master/Cython/Compiler/PyrexTypes.py#L5049)

So I wonder if a general direction makes sense? Would appreciate any sorts of pointers, really!

Cheers,

Evgeni

Or maybe I'm looking