From 05880da6911c366d6f9546fec448ae1b3e6e8b7b Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Thu, 3 Dec 2020 14:37:56 +1000
Subject: [PATCH] rand/distribution: allow rvalues for uniform distributions

---
 rand/distribution/uniform.hpp | 36 ++++++++++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 7 deletions(-)

diff --git a/rand/distribution/uniform.hpp b/rand/distribution/uniform.hpp
index a96c55fc..3ebdbfee 100644
--- a/rand/distribution/uniform.hpp
+++ b/rand/distribution/uniform.hpp
@@ -48,22 +48,34 @@ namespace cruft::rand::distribution {
         void reset (void);
 
 
+        // As a difference to libstd++ and libcxx we accept universal
+        // references as arguments; purely because it fits some of our
+        // existing code better, not because it's an efficient or desirable
+        // pattern.
         template <typename GeneratorT>
-        result_type operator() (GeneratorT &gen)
+        result_type operator() (GeneratorT &&gen)
         {
-            return this->template operator() (gen, m_param);
+            return this->template operator() (std::forward<GeneratorT> (gen), m_param);
         }
 
+
+        // As a difference to libstd++ and libcxx we accept universal
+        // references as arguments; purely because it fits some of our
+        // existing code better, not because it's an efficient or desirable
+        // pattern.
         template <typename GeneratorT>
         result_type
-        operator() (GeneratorT &gen, param_type const &p)
+        operator() (GeneratorT &&gen, param_type const &p)
         {
             // We use the same approach as libstdc++.
             //
             // Specialising for downscaling gen, upscaling gen, and identify
             // gen transforms.
 
-            using num_t = std::common_type_t<result_type, typename GeneratorT::result_type>;
+            using num_t = std::common_type_t<
+                result_type,
+                typename std::remove_cvref_t<GeneratorT>::result_type
+            >;
             num_t const gen_range = gen.max () - gen.min ();
             num_t const our_range = p.b - p.a;
 
@@ -168,6 +180,7 @@ namespace cruft::rand::distribution {
         return accum / base;
     }
 
+
     template <typename ResultT>
     struct uniform_real_distribution {
         static_assert (std::is_floating_point_v<ResultT>);
@@ -197,15 +210,24 @@ namespace cruft::rand::distribution {
         void reset (void);
 
 
+        // As a difference to libstd++ and libcxx we accept universal
+        // references as arguments; purely because it fits some of our
+        // existing code better, not because it's an efficient or desirable
+        // pattern.
         template <typename GeneratorT>
-        result_type operator() (GeneratorT &gen)
+        result_type operator() (GeneratorT &&gen)
         {
-            return this->template operator() (gen, m_param);
+            return this->template operator() (std::forward<GeneratorT> (gen), m_param);
         }
 
+
+        // As a difference to libstd++ and libcxx we accept universal
+        // references as arguments; purely because it fits some of our
+        // existing code better, not because it's an efficient or desirable
+        // pattern.
         template <typename GeneratorT>
         result_type
-        operator() (GeneratorT &gen, param_type const &p)
+        operator() (GeneratorT &&gen, param_type const &p)
         {
             return ::cruft::rand::distribution::generate_canonical<
                 result_type,