From: Alexander Grund (alexander.grund_at_[hidden])
Date: 2021-03-24 13:49:51
 I also do not even begin to understand why 'bool (*)(char const)'
becomes 'bool (*)(char)' in any logical world. Clearly a char const is
not the same as a char. Who in their right minds would make up a rule
that says they are the same, whether in a function declaration or not ?
They clearly are not, unless you are out to destroy the notion that
top-level consts in function declarations mean anything.
That is pretty easy: The function type(!) does NOT include the const of
value parameters. My goto for this is godbolt and an easy template test:
https://godbolt.org/z/7MvbWb3EW
This is why in the function declaration you can omit the const even when
you use it in the definition and if you think about it it makes sense:
If the function does or does not modify a copied (i.e. by-value)
parameter doesn't matter to the caller at all.
>
> Honestly if this is now C++, something seriously has gone wrong
> AFAICS. No doubt I am missing something basic, but this is truly
> "Alice in Wonderland" stuff to me. OK, I have had my rant. In what I
> was working on I will just specify that T as a top-level const is
> disallowed. My design can get by on that, rather than come up with
> some tortured code that allows T as a top-level const in the sort of
> signature above which works in both C++14 and C++17 on up.
In short the takeaway here is: Function value parameters in function
signatures are never const.