[Bug libstdc++/96731] uniform_int_distribution requirement that its type is_integral is too strict

[TonyELewis at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96731

--- Comment #5 from Tony E Lewis  ---
Thanks very much for your work on this.

That's a shame but I appreciate the problems you've highlighted.

> I don't plan to work on this any further for now.

Yes, fair enough.

[Bug libstdc++/96731] uniform_int_distribution requirement that its type is_integral is too strict

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96731

--- Comment #4 from Jonathan Wakely  ---
Created attachment 49135
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49135&action=edit
Patch to relax std::uniform_int_distribution requirements

This patch allows a custom integer-like type to be used with
std::uniform_int_distribution, but it's harder than it seems.

We need to use std::make_unsigned, which is undefined for non-integral types.
The patch will use _IntType is numeric_limits<_IntType>::is_signed is false,
otherwise it will use make_unsigned_t<_IntType> if possible, and unsigned long
long otherwise.

But the example still fails, because std::sample also requires an integral
type, and also wants to use make_unsigned. And the standard is clear that it's
not just undefined, but ill-formed and requires a diagnostic:

> Mandates: For the overload in namespace std, Distance is an integer type

I don't plan to work on this any further for now.

[Bug libstdc++/96731] uniform_int_distribution requirement that its type is_integral is too strict

[TonyELewis at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96731

--- Comment #3 from Tony E Lewis  ---
Thanks for correcting my failure to find the relevant part of the standard and
for confirming this as an enhancement request.

Yes please. If libstdc++'s sample() could play nicely with range-v3's
view::indices, that'd be much appreciated.

[Bug libstdc++/96731] uniform_int_distribution requirement that its type is_integral is too strict

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96731

Jonathan Wakely  changed:

   What|Removed |Added

 Ever confirmed|0   |1
 Status|UNCONFIRMED |NEW
   Severity|normal  |enhancement
   Last reconfirmed||2020-08-21

--- Comment #2 from Jonathan Wakely  ---
Since it's undefined, we can do whatever we want, including causing compilation
to fail with a static_assert, or ignoring it (as libc++ seems to do), or using
another condition to check for sufficiently integer-like types (possibly only
in non-strict modes).

Confirming as an enhancement request.

[Bug libstdc++/96731] uniform_int_distribution requirement that its type is_integral is too strict

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96731

--- Comment #1 from Jonathan Wakely  ---
(In reply to Tony E Lewis from comment #0)
> I can't see any obvious mention of constraints on
> uniform_­int_­distribution's IntType in
> http://eel.is/c++draft/rand.dist.uni.int

See http://eel.is/c++draft/rand#req.genl-1.5