"Effective Modern C++" study notes clause two: understand auto type derivation

First, auto type deduction is exactly the same as template type deduction . The only difference is that when deducing the expression enclosed in curly braces, auto will deduct it into a type of std::initializer_list. The code example is as follows:

auto x1 = 27;    //x1型别为int
auto x2(27);     //x2型别为int
auto x3 = {27};  //x3型别为std::initializer_list<int>
auto x4{27};     //x4型别为std::initializer_list<int>

auto x5 = {27,13,0.5};     //x5型别无法推导，编译报错，因为里面包含两种数据类型

Shorthand

• The auto type deduction is exactly the same as the template type deduction . The only difference is that when the expression enclosed in curly braces is deduced, auto deduces it to a type of std::initializer_list.
• Using auto in the return value of a function or lambda expression will use template deduction instead of auto deduction