Remove old is_constructible workarounds and replace typedefs with using

include/fmt/printf.h

@@ -329,12 +329,9 @@ template <typename T> struct printf_formatter {
 template <typename OutputIt, typename Char> class basic_printf_context {
  public:
   /** The character type for the output. */
-  typedef Char char_type;
-  typedef basic_format_arg<basic_printf_context> format_arg;
-
-  template <typename T> struct formatter_type {
-    typedef printf_formatter<T> type;
-  };
+  using char_type = Char;
+  using format_arg = basic_format_arg<basic_printf_context>;
+  template <typename T> using formatter_type = printf_formatter<T>;
 
  private:
   typedef basic_format_specs<char_type> format_specs;

test/core-test.cc

@@ -209,17 +209,15 @@ struct custom_context {
   typedef char char_type;
 
   template <typename T> struct formatter_type {
-    struct type {
-      template <typename ParseContext>
-      auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
-        return ctx.begin();
-      }
-
-      const char* format(const T&, custom_context& ctx) {
-        ctx.called = true;
-        return nullptr;
-      }
-    };
+    template <typename ParseContext>
+    auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
+      return ctx.begin();
+    }
+
+    const char* format(const T&, custom_context& ctx) {
+      ctx.called = true;
+      return nullptr;
+    }
   };
 
   bool called;