X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=folly%2FFormat.h;h=3837d1079e9636b31d529a32d39f990e0805057d;hb=598926c4529b459ce535657ec76ac792f4ec010e;hp=7c9929a9751411826d7b42a979e1b6090afb717d;hpb=e8d259542762e9611ce98724b14510c88dfa91dd;p=folly.git

diff --git a/folly/Format.h b/folly/Format.h
index 7c9929a9..3837d107 100644
--- a/folly/Format.h
+++ b/folly/Format.h
@@ -46,14 +46,15 @@ class FormatValue;
 // meta-attribute to identify formatters in this sea of template weirdness
 namespace detail {
 class FormatterTag {};
-};
+} // namespace detail
 
 /**
  * Formatter class.
  *
- * Note that this class is tricky, as it keeps *references* to its arguments
- * (and doesn't copy the passed-in format string).  Thankfully, you can't use
- * this directly, you have to use format(...) below.
+ * Note that this class is tricky, as it keeps *references* to its lvalue
+ * arguments (while it takes ownership of the temporaries), and it doesn't
+ * copy the passed-in format string. Thankfully, you can't use this
+ * directly, you have to use format(...) below.
  */
 
 /* BaseFormatter class.
@@ -103,14 +104,13 @@ class BaseFormatter {
   }
 
   /**
-   * metadata to identify generated children of BaseFormatter
+   * Metadata to identify generated children of BaseFormatter
    */
   typedef detail::FormatterTag IsFormatter;
   typedef BaseFormatter BaseType;
 
  private:
-  typedef std::tuple<FormatValue<typename std::decay<Args>::type>...>
-      ValueTuple;
+  typedef std::tuple<Args...> ValueTuple;
   static constexpr size_t valueCount = std::tuple_size<ValueTuple>::value;
 
   Derived const& asDerived() const {
@@ -166,7 +166,7 @@ class BaseFormatter {
       K<valueCount, int>::type getSizeArgFrom(size_t i, const FormatArg& arg)
           const {
     if (i == K) {
-      return getValue(std::get<K>(values_), arg);
+      return getValue(getFormatValue<K>(), arg);
     }
     return getSizeArgFrom<K + 1>(i, arg);
   }
@@ -188,10 +188,19 @@ class BaseFormatter {
   // for the exclusive use of format() (below).  This way, you can't create
   // a Formatter object, but can handle references to it (for streaming,
   // conversion to string, etc) -- which is good, as Formatter objects are
-  // dangerous (they hold references, possibly to temporaries)
+  // dangerous (they may hold references).
   BaseFormatter(BaseFormatter&&) = default;
   BaseFormatter& operator=(BaseFormatter&&) = default;
 
+  template <size_t K>
+  using ArgType = typename std::tuple_element<K, ValueTuple>::type;
+
+  template <size_t K>
+  FormatValue<typename std::decay<ArgType<K>>::type> getFormatValue() const {
+    return FormatValue<typename std::decay<ArgType<K>>::type>(
+        std::get<K>(values_));
+  }
+
   ValueTuple values_;
 };
 
@@ -213,7 +222,7 @@ class Formatter : public BaseFormatter<
 
   template <size_t K, class Callback>
   void doFormatArg(FormatArg& arg, Callback& cb) const {
-    std::get<K>(this->values_).format(arg, cb);
+    this->template getFormatValue<K>().format(arg, cb);
   }
 
   friend class BaseFormatter<
@@ -313,7 +322,7 @@ struct DefaultValueWrapper {
   const Container& container;
   const Value& defaultValue;
 };
-} // namespace
+} // namespace detail
 
 template <class Container, class Value>
 detail::DefaultValueWrapper<Container, Value> defaulted(
@@ -423,7 +432,7 @@ struct IsFormatter<
     typename std::enable_if<
         std::is_same<typename T::IsFormatter, detail::FormatterTag>::value>::
         type> : public std::true_type {};
-} // folly::detail
+} // namespace detail
 
 // Deprecated API. formatChecked() et. al. now behave identically to their
 // non-Checked counterparts.