A similar defect that was "fixed" breaking backward compatibility was the resolution of initializer_list constructors of recursive types: T(initializer_list<

A similar defect that was "fixed" breaking backward compatibility was the resolution of initializer_list constructors of recursive types: T(initializer_list<T>); Before, if you did T element; T list = {element}; the second initialization would be dispatched to the initializer_list constructor; after the fix (for GCC, after 4.9) it would call the copy constructor. See http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1467 http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html... . For us, this changed the semantics of folly::dynamic, which used the initializer_list constructor to construct lists: dynamic element = "hello"; dynamic list = {element}; // ["hello"] before, "hello" after We had to deprecate the initializer_list constructor and fix all the occurrences (https://github.com/facebook/folly/commit/07dc3ce5923b2d761ca9fd7cd53ee890a4ad839d https://github.com/facebook/folly/commit/07dc3ce5923b2d761ca..., https://github.com/facebook/folly/commit/d458b0a14486b9d80d5644c7b4de60640c891df1 https://github.com/facebook/folly/commit/d458b0a14486b9d80d5...).