From fb7c98948735343095414ca2c5462af2304883a4 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Wed, 19 Dec 2018 17:12:28 +1100
Subject: [PATCH] view: allow construction from anything that has begin/end

---
 view.hpp | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/view.hpp b/view.hpp
index 11c85a21..8415263a 100644
--- a/view.hpp
+++ b/view.hpp
@@ -44,18 +44,28 @@ namespace cruft {
             m_end   (last)
         { ; }
 
+
         template <
             typename ContainerT,
-            typename = std::enable_if_t<is_container_v<std::decay_t<ContainerT>>,void>
+            typename = std::void_t<
+                decltype (std::declval<ContainerT&> ().begin ()),
+                decltype (std::declval<ContainerT&> ().end   ())
+            >
         >
-        view (ContainerT &rhs):
-            view (rhs.begin (), rhs.end ())
+        view (ContainerT &rhs) noexcept (
+            noexcept (std::declval<ContainerT> ().begin ()) &&
+            noexcept (std::declval<ContainerT> ().end   ())
+        )
+        : view (rhs.begin (), rhs.end ())
         { ; }
 
 
         template <
             typename ContainerT,
-            typename = std::enable_if_t<is_container_v<std::decay_t<ContainerT>>,void>
+            typename = std::void_t<
+                decltype (std::declval<ContainerT const&> ().begin ()),
+                decltype (std::declval<ContainerT const&> ().end   ())
+            >
         >
         view (const ContainerT &rhs):
             view (rhs.begin (), rhs.end ())
@@ -447,12 +457,14 @@ namespace cruft {
 
     template <typename ContainerT>
     view (ContainerT&) -> view<
-        typename ContainerT::iterator
+        decltype (std::declval<ContainerT&> ().begin ()),
+        decltype (std::declval<ContainerT&> ().end   ())
     >;
 
     template <typename ContainerT>
     view (const ContainerT&) -> view<
-        typename ContainerT::const_iterator
+        decltype (std::declval<ContainerT const&> ().begin ()),
+        decltype (std::declval<ContainerT const&> ().end   ())
     >;
 
     // base + count constructor