Various noexcept specifiers for swap methods

Summary: Pull Request resolved: https://github.com/facebook/folly/pull/944

Reviewed By: Orvid

Differential Revision: D10231693

Pulled By: yfeldblum

fbshipit-source-id: 9c0c5d7c4c1e4d9d9860c71e608e47d661a41fdd

folly/File.cpp

@@ -93,13 +93,13 @@ int File::release() noexcept {
   return released;
 }
 
-void File::swap(File& other) {
+void File::swap(File& other) noexcept {
   using std::swap;
   swap(fd_, other.fd_);
   swap(ownsFd_, other.ownsFd_);
 }
 
-void swap(File& a, File& b) {
+void swap(File& a, File& b) noexcept {
   a.swap(b);
 }
 

folly/File.h

@@ -119,7 +119,7 @@ class File {
   /**
    * Swap this File with another.
    */
-  void swap(File& other);
+  void swap(File& other) noexcept;
 
   // movable
   File(File&&) noexcept;
@@ -153,6 +153,6 @@ class File {
   bool ownsFd_;
 };
 
-void swap(File& a, File& b);
+void swap(File& a, File& b) noexcept;
 
 } // namespace folly

folly/experimental/StringKeyedMap.h

@@ -191,9 +191,7 @@ class StringKeyedMap : private std::map<StringPiece, Value, Compare, Alloc> {
     Base::clear();
   }
 
-  void swap(StringKeyedMap& other) & {
-    return Base::swap(other);
-  }
+  using Base::swap;
 
   ~StringKeyedMap() {
     // Here we assume that map doesn't use keys in destructor