Workaround for -Werror,-Wambiguous-reversed-operator

Summary: Workaround for -Werror,-Wambiguous-reversed-operator

Reviewed By: yfeldblum, mpark

Differential Revision: D31615526

fbshipit-source-id: 23f72e7b0aaea65d1e0cc294beef3b33d7aa985e

folly/detail/Iterators.h

@@ -79,30 +79,9 @@ class IteratorFacade {
   using difference_type = ssize_t;
   using iterator_category = Tag;
 
-  bool operator==(D const& rhs) const { return asDerivedConst().equal(rhs); }
+  friend bool operator==(D const& lhs, D const& rhs) { return equal(lhs, rhs); }
 
-  bool operator!=(D const& rhs) const { return !operator==(rhs); }
-
-  /*
-   * Allow for comparisons between this and an iterator of some other class.
-   * (e.g. a const_iterator version of this, the probable use case).
-   * Does a conversion of D (or D reference) to D2, if one exists (otherwise
-   * this is disabled).  Disabled if D and D2 are the same, to disambiguate
-   * this and the `operator==(D const&) const` method above.
-   */
-
-  template <
-      class D2,
-      std::enable_if_t<!std::is_same<D, D2>::value, int> = 0,
-      std::enable_if_t<std::is_convertible<D, D2>::value, int> = 0>
-  bool operator==(D2 const& rhs) const {
-    return D2(asDerivedConst()) == rhs;
-  }
-
-  template <class D2>
-  bool operator!=(D2 const& rhs) const {
-    return !operator==(rhs);
-  }
+  friend bool operator!=(D const& lhs, D const& rhs) { return !(lhs == rhs); }
 
   V& operator*() const { return asDerivedConst().dereference(); }
 
@@ -134,6 +113,8 @@ class IteratorFacade {
   D& asDerived() { return static_cast<D&>(*this); }
 
   D const& asDerivedConst() const { return static_cast<D const&>(*this); }
+
+  static bool equal(D const& lhs, D const& rhs) { return lhs.equal(rhs); }
 };
 
 /**