segments mandates use static_assert

fix #521

include/boost/url/impl/segments_encoded_ref.hpp

@@ -13,10 +13,8 @@
 
 #include <boost/url/detail/config.hpp>
 #include <boost/url/detail/segments_iter_impl.hpp>
-#include <boost/url/string_view.hpp>
-#include <boost/url/detail/except.hpp>
 #include <boost/url/detail/any_segments_iter.hpp>
-#include <iterator>
+#include <type_traits>
 
 namespace boost {
 namespace urls {
@@ -36,15 +34,23 @@ clear() noexcept
 }
 
 template<class FwdIt>
-auto
+void
 segments_encoded_ref::
-assign(FwdIt first, FwdIt last) ->
-    typename std::enable_if<
-        std::is_convertible<typename
-            std::iterator_traits<
-                FwdIt>::reference,
-            pct_string_view>::value>::type
+assign(
+    FwdIt first, FwdIt last)
 {
+/*  If you get a compile error here, it
+    means that the iterators you passed
+    do not meet the requirements stated
+    in the documentation.
+*/
+    static_assert(
+        std::is_convertible<
+            typename std::iterator_traits<
+                FwdIt>::reference,
+            string_view>::value,
+        "Type requirements not met");
+
     u_->edit_segments(
         begin().it_,
         end().it_,
@@ -59,14 +65,24 @@ insert(
     iterator before,
     FwdIt first,
     FwdIt last) ->
-        typename std::enable_if<
-            std::is_convertible<typename
-                std::iterator_traits<
-                    FwdIt>::reference,
-                pct_string_view>::value,
-            iterator>::type
+        iterator
 {
-    return insert(before, first, last,
+/*  If you get a compile error here, it
+    means that the iterators you passed
+    do not meet the requirements stated
+    in the documentation.
+*/
+    static_assert(
+        std::is_convertible<
+            typename std::iterator_traits<
+                FwdIt>::reference,
+            string_view>::value,
+        "Type requirements not met");
+
+    return insert(
+        before,
+        first,
+        last,
         typename std::iterator_traits<
             FwdIt>::iterator_category{});
 }
@@ -89,13 +105,20 @@ replace(
     iterator to,
     FwdIt first,
     FwdIt last) ->
-        typename std::enable_if<
-            std::is_convertible<typename
-                std::iterator_traits<
-                    FwdIt>::reference,
-                pct_string_view>::value,
-            iterator>::type
+        iterator
 {
+/*  If you get a compile error here, it
+    means that the iterators you passed
+    do not meet the requirements stated
+    in the documentation.
+*/
+    static_assert(
+        std::is_convertible<
+            typename std::iterator_traits<
+                FwdIt>::reference,
+            string_view>::value,
+        "Type requirements not met");
+
     return u_->edit_segments(
         from.it_,
         to.it_,

include/boost/url/impl/segments_ref.hpp

@@ -12,9 +12,9 @@
 #define BOOST_URL_IMPL_SEGMENTS_REF_HPP
 
 #include <boost/url/detail/config.hpp>
-#include <boost/url/segments_base.hpp>
 #include <boost/url/detail/any_segments_iter.hpp>
-#include <iterator>
+#include <boost/url/detail/segments_iter_impl.hpp>
+#include <type_traits>
 
 namespace boost {
 namespace urls {
@@ -34,15 +34,22 @@ clear() noexcept
 }
 
 template<class FwdIt>
-auto
+void
 segments_ref::
-assign(FwdIt first, FwdIt last) ->
-    typename std::enable_if<
-        std::is_convertible<typename
-            std::iterator_traits<
-                FwdIt>::reference,
-            string_view>::value>::type
+assign(FwdIt first, FwdIt last)
 {
+/*  If you get a compile error here, it
+    means that the iterators you passed
+    do not meet the requirements stated
+    in the documentation.
+*/
+    static_assert(
+        std::is_convertible<
+            typename std::iterator_traits<
+                FwdIt>::reference,
+            string_view>::value,
+        "Type requirements not met");
+
     u_->edit_segments(
         begin().it_,
         end().it_,
@@ -57,13 +64,20 @@ insert(
     iterator before,
     FwdIt first,
     FwdIt last) ->
-        typename std::enable_if<
-            std::is_convertible<typename
-                std::iterator_traits<
-                    FwdIt>::reference,
-                string_view>::value,
-            iterator>::type
+        iterator
 {
+/*  If you get a compile error here, it
+    means that the iterators you passed
+    do not meet the requirements stated
+    in the documentation.
+*/
+    static_assert(
+        std::is_convertible<
+            typename std::iterator_traits<
+                FwdIt>::reference,
+            string_view>::value,
+        "Type requirements not met");
+
     return insert(
         before,
         first,
@@ -90,13 +104,20 @@ replace(
     iterator to,
     FwdIt first,
     FwdIt last) ->
-        typename std::enable_if<
-            std::is_convertible<typename
-                std::iterator_traits<
-                    FwdIt>::reference,
-                string_view>::value,
-            iterator>::type
+        iterator
 {
+/*  If you get a compile error here, it
+    means that the iterators you passed
+    do not meet the requirements stated
+    in the documentation.
+*/
+    static_assert(
+        std::is_convertible<
+            typename std::iterator_traits<
+                FwdIt>::reference,
+            string_view>::value,
+        "Type requirements not met");
+
     return u_->edit_segments(
         from.it_,
         to.it_,

include/boost/url/segments_encoded_ref.hpp

@@ -14,6 +14,7 @@
 #include <boost/url/detail/config.hpp>
 #include <boost/url/segments_encoded_base.hpp>
 #include <initializer_list>
+#include <iterator>
 
 namespace boost {
 namespace urls {
@@ -358,15 +359,7 @@ public:
         to assign.
     */
     template<class FwdIt>
-#ifdef BOOST_URL_DOCS
     void
-#else
-    typename std::enable_if<
-        std::is_convertible<typename
-            std::iterator_traits<
-                FwdIt>::reference,
-            pct_string_view>::value>::type
-#endif
     assign(FwdIt first, FwdIt last);
 
     //--------------------------------------------
@@ -509,16 +502,7 @@ public:
         to insert.
     */
     template<class FwdIt>
-#ifdef BOOST_URL_DOCS
     iterator
-#else
-    typename std::enable_if<
-        std::is_convertible<typename
-            std::iterator_traits<
-                FwdIt>::reference,
-            pct_string_view>::value,
-        iterator>::type
-#endif
     insert(
         iterator before,
         FwdIt first,
@@ -729,16 +713,7 @@ public:
         @param first, last The range of segments to assign.
     */
     template<class FwdIt>
-#ifdef BOOST_URL_DOCS
     iterator
-#else
-    typename std::enable_if<
-        std::is_convertible<typename
-            std::iterator_traits<
-                FwdIt>::reference,
-            pct_string_view>::value,
-        iterator>::type
-#endif
     replace(
         iterator from,
         iterator to,

include/boost/url/segments_ref.hpp

@@ -344,15 +344,7 @@ public:
         to assign.
     */
     template<class FwdIt>
-#ifdef BOOST_URL_DOCS
     void
-#else
-    typename std::enable_if<
-        std::is_convertible<typename
-            std::iterator_traits<
-                FwdIt>::reference,
-            string_view>::value>::type
-#endif
     assign(FwdIt first, FwdIt last);
 
     //--------------------------------------------
@@ -479,16 +471,7 @@ public:
         to insert.
     */
     template<class FwdIt>
-#ifdef BOOST_URL_DOCS
     iterator
-#else
-    typename std::enable_if<
-        std::is_convertible<typename
-            std::iterator_traits<
-                FwdIt>::reference,
-            string_view>::value,
-        iterator>::type
-#endif
     insert(
         iterator before,
         FwdIt first,
@@ -682,16 +665,7 @@ public:
         @param first, last The range of segments to assign.
     */
     template<class FwdIt>
-#ifdef BOOST_URL_DOCS
     iterator
-#else
-    typename std::enable_if<
-        std::is_convertible<typename
-            std::iterator_traits<
-                FwdIt>::reference,
-            string_view>::value,
-        iterator>::type
-#endif
     replace(
         iterator from,
         iterator to,