fix: #159 Merge branch 'conversion-precedence'

.github/workflows/main.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         # g++-4.8 and 4.9 are tested on Travis.CI.
-        compiler: ['g++-9', 'g++-8', 'g++-7', 'g++-6', 'g++-5']
+        compiler: ['g++-11', 'g++-10', 'g++-9', 'g++-8', 'g++-7', 'g++-6', 'g++-5']
         standard: ['11', '14', '17', '20']
         exclude:
             - {compiler: 'g++-5', standard: '17'}
@@ -59,6 +59,7 @@ jobs:
             - {compiler: '6.0', standard: '20'}
             - {compiler: '7',   standard: '20'}
             - {compiler: '8',   standard: '20'}
+            - {compiler: '9',   standard: '20'}
     steps:
       - name: Checkout
         uses: actions/checkout@v2

toml/get.hpp

@@ -255,16 +255,19 @@ get(const basic_value<C, M, V>&);
 
 // toml::from<T>::from_toml(v)
 template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V,
-         std::size_t S = sizeof(::toml::from<T>)>
-T get(const basic_value<C, M, V>&);
+         template<typename ...> class M, template<typename ...> class V>
+detail::enable_if_t<detail::has_specialized_from<T>::value, T>
+get(const basic_value<C, M, V>&);
 
-// T(const toml::value&) and T is not toml::basic_value
+// T(const toml::value&) and T is not toml::basic_value,
+// and it does not have `from<T>` nor `from_toml`.
 template<typename T, typename C,
          template<typename ...> class M, template<typename ...> class V>
 detail::enable_if_t<detail::conjunction<
     detail::negation<detail::is_basic_value<T>>,
-    std::is_constructible<T, const basic_value<C, M, V>&>
+    std::is_constructible<T, const basic_value<C, M, V>&>,
+    detail::negation<detail::has_from_toml_method<T, C, M, V>>,
+    detail::negation<detail::has_specialized_from<T>>
     >::value, T>
 get(const basic_value<C, M, V>&);
 
@@ -440,9 +443,9 @@ get(const basic_value<C, M, V>& v)
     return ud;
 }
 template<typename T, typename C,
-         template<typename ...> class M, template<typename ...> class V,
-         std::size_t>
-T get(const basic_value<C, M, V>& v)
+         template<typename ...> class M, template<typename ...> class V>
+detail::enable_if_t<detail::has_specialized_from<T>::value, T>
+get(const basic_value<C, M, V>& v)
 {
     return ::toml::from<T>::from_toml(v);
 }
@@ -450,8 +453,10 @@ T get(const basic_value<C, M, V>& v)
 template<typename T, typename C,
          template<typename ...> class M, template<typename ...> class V>
 detail::enable_if_t<detail::conjunction<
-    detail::negation<detail::is_basic_value<T>>,
-    std::is_constructible<T, const basic_value<C, M, V>&>
+    detail::negation<detail::is_basic_value<T>>,                // T is not a toml::value
+    std::is_constructible<T, const basic_value<C, M, V>&>,      // T is constructible from toml::value
+    detail::negation<detail::has_from_toml_method<T, C, M, V>>, // and T does not have T.from_toml(v);
+    detail::negation<detail::has_specialized_from<T>>           // and T does not have toml::from<T>{};
     >::value, T>
 get(const basic_value<C, M, V>& v)
 {

toml/traits.hpp

@@ -2,6 +2,10 @@
 // Distributed under the MIT License.
 #ifndef TOML11_TRAITS_HPP
 #define TOML11_TRAITS_HPP
+
+#include "from.hpp"
+#include "into.hpp"
+
 #include <chrono>
 #include <forward_list>
 #include <string>
@@ -84,6 +88,22 @@ struct has_into_toml_method_impl
     static std::false_type check(...);
 };
 
+struct has_specialized_from_impl
+{
+    template<typename T>
+    static std::false_type check(...);
+    template<typename T, std::size_t S = sizeof(::toml::from<T>)>
+    static std::true_type check(::toml::from<T>*);
+};
+struct has_specialized_into_impl
+{
+    template<typename T>
+    static std::false_type check(...);
+    template<typename T, std::size_t S = sizeof(::toml::into<T>)>
+    static std::true_type check(::toml::from<T>*);
+};
+
+
 /// Intel C++ compiler can not use decltype in parent class declaration, here
 /// is a hack to work around it. https://stackoverflow.com/a/23953090/4692076
 #ifdef __INTEL_COMPILER
@@ -114,6 +134,11 @@ template<typename T>
 struct has_into_toml_method
 : decltype(has_into_toml_method_impl::check<T>(nullptr)){};
 
+template<typename T>
+struct has_specialized_from : decltype(has_specialized_from_impl::check<T>(nullptr)){};
+template<typename T>
+struct has_specialized_into : decltype(has_specialized_into_impl::check<T>(nullptr)){};
+
 #ifdef __INTEL_COMPILER
 #undef decltype
 #endif