Modern C++ Programming Cookbook

There's more

The following sample shows several examples of direct-list-initialization and copy-list-initialization. In C++11, the deduced type of all these expressions is std::initializer_list<int>.

auto a = {42};   // std::initializer_list<int>auto b {42};     // std::initializer_list<int>auto c = {4, 2}; // std::initializer_list<int>auto d {4, 2};   // std::initializer_list<int>

C++17 has changed the rules for list initialization, differentiating between the direct- and copy-list-initialization. The new rules for type deduction are as follows:

• for copy list initialization auto deduction will deduce a std::initializer_list<T> if all elements in the list have the same type, or be ill-formed.
• for direct list initialization auto deduction will ...