Fixes const iteration for chain()

Fixes #65

Author: ryanhaining

chain.hpp

@@ -25,6 +25,16 @@ namespace iter {
     // rather than a chain function, use a callable object to support
     // from_iterable
     class ChainMaker;
+
+    template <typename>
+    struct AsTupleOfConstImpl;
+
+    template <typename... Ts>
+    struct AsTupleOfConstImpl<std::tuple<Ts...>>
+        : type_is<std::tuple<AsConst<Ts>...>> {};
+
+    template <typename T>
+    using AsTupleOfConst = typename AsTupleOfConstImpl<T>::type;
   }
 }
 
@@ -169,12 +179,12 @@ class iter::impl::Chained {
         {get_end(std::get<Is>(tup_))...}};
   }
 
-  Iterator<AsConst<TupType>> begin() const {
+  Iterator<AsTupleOfConst<TupType>> begin() const {
     return {0, {get_begin(std::as_const(std::get<Is>(tup_)))...},
         {get_end(std::as_const(std::get<Is>(tup_)))...}};
   }
 
-  Iterator<AsConst<TupType>> end() const {
+  Iterator<AsTupleOfConst<TupType>> end() const {
     return {sizeof...(Is), {get_end(std::as_const(std::get<Is>(tup_)))...},
         {get_end(std::as_const(std::get<Is>(tup_)))...}};
   }

test/test_chain.cpp

@@ -10,8 +10,8 @@
 #include "catch.hpp"
 
 using iter::chain;
-using itertest::SolidInt;
 using itertest::BasicIterable;
+using itertest::SolidInt;
 using Vec = const std::vector<char>;
 
 TEST_CASE("chain: three strings", "[chain]") {
@@ -28,8 +28,8 @@ TEST_CASE("chain: three strings", "[chain]") {
 
 TEST_CASE("chain: const iteration", "[chain][const]") {
   std::string s1{"abc"};
-  /* const */ std::string s2{"mno"};
-  auto ch = chain(s1, s2, std::string{"xyz"});
+  const std::string s2{"mno"};
+  const auto ch = chain(s1, s2, std::string{"xyz"});
 
   Vec v(std::begin(ch), std::end(ch));
   Vec vc{'a', 'b', 'c', 'm', 'n', 'o', 'x', 'y', 'z'};
@@ -309,8 +309,8 @@ template <typename T>
 using ImpT2 = decltype(chain.from_iterable(std::declval<T>()));
 TEST_CASE("chain.from_iterable: has correct ctor and assign ops",
     "[chain.from_iterable]") {
-  REQUIRE(itertest::IsMoveConstructibleOnly<ImpT2<std::vector<std::string>>>::
-          value);
-  REQUIRE(itertest::IsMoveConstructibleOnly<ImpT2<std::vector<std::string>&>>::
-          value);
+  REQUIRE(itertest::IsMoveConstructibleOnly<
+      ImpT2<std::vector<std::string>>>::value);
+  REQUIRE(itertest::IsMoveConstructibleOnly<
+      ImpT2<std::vector<std::string>&>>::value);
 }